The Subaru Telescope atop Mauna Kea. CHARIS works in conjunction with Subaru. Image: Dr. Hideaki Fujiwara - Subaru Telescope, NAOJ.
The revelation that there are thousands of planets out there, orbiting other stars, is mostly due to the success of the Kepler mission. But now that we know these exoplanets are there, we want to know all about them. We want to know their mass, their temperature, how old they are, and pretty much everything else about them.
Now, a new instrument called the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) has captured the light from one of those exoplanets. This has the researchers excited about what they can see.
“We couldn’t have been more pleased by the results.” – N. Jeremy Kasdin
CHARIS allows astronomers to isolate light reflecting from planets. That’s difficult to do, since they are so much dimmer than the stars they orbit. CHARIS is able to isolate the reflective light from planets larger than Jupiter. Then astronomers can analyze that light to learn about the planet’s age, atmospheric composition, and its size.
“By analyzing the spectrum of a planet, we can really understand a lot about the planet. You can see specific features that can allow you to understand the mass, the temperature, the age of the planet.” – team member Tyler Groff
This image from the CHARIS instrument shows planets located around a star in the planetary system HR8799. Image: N. Jeremy Kasdin and team.
CHARIS was designed and built by a team led by N. Jeremy Kasdin, a professor of mechanical and aerospace engineering at Princeton University. It took them five years to build CHARIS.
The spectrograph sits inside a 500 lb case that measures 30x30x12. Inside that case, it’s kept at -223.15 Celsius (50 Kelvin, -369 F.) The CHARIS instrument has nine mirrors, five filters, two prism assemblies and a microlens array. The microlens array is a special optical device with an array of tiny lenses etched into its surface.
During a CHARIS field test, researchers captured images of celestial objects, including vapor clouds moving across a section of the planet Neptune. (Images courtesy of N. Jeremy Kasdin and the research team)
CHARIS works in conjunction with the Subaru Telescope in Hawaii. It’s part of a long-time collaboration between Princeton, the University of Tokyo and the National Astronomical Observatory of Japan, which operates the Subaru Telescope at Mauna Kea, Hawaii. And these first results are generating a lot of interest.
According to Tyler Groff, a team member from Princeton who now works for NASA, the preliminary result from CHARIS have generated a lot of interest from the astronomy community. The CHARIS team is now reviewing research proposals.
“There is a lot of excitement,” Groff said. “Charis is going to open for science in February to everyone.”
CHARIS is designed to capture the light from distant exoplanets, so its field of view is tiny. It’s only 2 arc-seconds, which is a tiny patch of sky. For reference, the full Moon is about 1,800 arc-seconds. But it can take images across a wide band of light wavelengths. The fact that it captures such a wide band of light is what allows such detailed analysis of anything it’s pointed at.
“We tested CHARIS on Neptune, but the entire planet doesn’t even fit on our detector.” -Tyler Groff
CHARIS is located behind a coronagraph. The coronagraph channels light from the Subaru Telescope and divides the light coming directly from a star from the light that is reflecting off planets orbiting that star. The team says it’s like picking out the light reflecting from a speck of tinsel floating in front of a spotlight that’s hundreds of miles away.
This artist's illustration shows a planet circling a pair of distant red dwarf stars, representing the the system OGLE-2007-BLG-349 system, about 8,000 lightyears from Earth. Credit: NASA, ESA, and G. Bacon (STScI).
Binary stars are common throughout the galaxy, as it has been estimated about half the stars in our sky consist of two stars orbiting each other. Therefore, it’s also thought that about half of all exoplanet host stars are binaries as well. However, only about 10 of these so called circumbinary planets have been found so far in the 3,000-plus confirmed extrasolar planets that have been discovered.
But chalk up one more circumbinary planet, and this one bodes well for a technique that could help scientists find planets that orbit far away from their stars. Astronomers using the Hubble Space Telescope have confirmed a very interesting “three-body” system where two very close stars have a planet that orbits them both at a rather large distance.
The two red dwarf stars are just 7 million miles apart, or about 14 times the diameter of the Moon’s orbit around Earth. The planet orbits roughly 300 million miles from the stellar duo, about the distance of the asteroid belt from the Sun. The planet completes an orbit around both stars roughly every seven years.
The Hubble Space Telescope. Image: NASA
Hubble used the a technique called gravitational microlensing, where the gravity of a foreground star bends and amplifies the light of a background star that momentarily aligns with it. The light magnification can reveal clues to the nature of the foreground star and any associated planets.
The system, called OGLE-2007-BLG-349, was originally detected in 2007 by the Optical Gravitational Lensing Experiment (OGLE), a telescope at the Las Campanas Observatory in Chile that searches for and observes microlensing effects from small distortions of spacetime, caused by stars and exoplanets.
However, the original OGLE observations could not confirm the details of the OGLE-2007-BLG-349 system. OGLE and several other ground-based observations determined there was a star and a planet in this system, but they couldn’t positively identify what the observed third body was.
“The ground-based observations suggested two possible scenarios for the three-body system: a Saturn-mass planet orbiting a close binary star pair or a Saturn-mass and an Earth-mass planet orbiting a single star,” said David Bennett, from NASA’s Goddard Space Flight Center, who is the first author in a new paper about the system, to be published in the Astrophysical Journal.
With Hubble’s sharp eyesight, the research team was able to separate the background source star and the lensing star from their neighbors in the very crowded star field. The Hubble observations revealed that the starlight from the foreground lens system was too faint to be a single star, but it had the brightness expected for two closely orbiting red dwarf stars, which are fainter and less massive than our sun.
“So, the model with two stars and one planet is the only one consistent with the Hubble data,” Bennett said.
“OGLE has detected over 17,000 microlensing events, but this is the first time such an event has been caused by a circumbinary planetary system,” explains Andrzej Udalski from the University of Warsaw, Poland, co-author of the study and leader of the OGLE project.
The team said this first-ever confirmation of an exoplanet system using the gravitational microlensing technique suggests some intriguing possibilities. While data from the Kepler Space Telescope is more likely to reveal planets that orbit close to their stars, microlensing allows planets to be found at distances far from their host stars.
“This discovery, suggests we need to rethink our observing strategy when it comes to stellar binary lensing events,” said Yiannis Tsapras, another member of the team, from the Astronomisches Recheninstitut in Heidelberg, Germany. “This is an exciting new discovery for microlensing”.
The team said that since this observation has shown that microlensing can successfully detect circumbinary planets, Hubble could provide an essential new role in the continued search for exoplanets.
OGLE-2007-BLG-349 is located 8,000 light-years away, towards the center of our galaxy.
(And, you’re welcome… I didn’t mention Tatooine in this article, until now!)
Artist’s conception of the binary system with three giant planets discovered in this study. One star hosts two planets and the other hosts the third. The system represents the smallest-separation binary in which both stars host planets that has ever been observed. Image courtesy of Robin Dienel/Carnegie.
The more we look, the more we see the great diversity in planetary systems around other stars. And curiously, planet hunters are finding that most star systems are very different from our own.
An example is a recently discovered system that is extremely crowded. It consists of a three giant planets in a binary (two stars) system. One star hosts two planets and the other hosts the third. The system represents the smallest-separation binary in which both stars host planets that has ever been observed.
“The probability of finding a system with all these components was extremely small,” said Johanna Teske from the Carnegie Institution for Science, “so these results will serve as an important benchmark for understanding planet formation, especially in binary systems.”
An illustration of this highly unusual system, which features the smallest-separation binary stars that both host planets ever discovered. Only six other metal-poor binary star systems with exoplanets have ever been found. Illustration courtesy of Timothy Rodigas/Carnegie.
Teske and her team said this busy system might help explain the influence that giant planets like Jupiter have over a solar system’s architecture.
“We are trying to figure out if giant planets like Jupiter often have long and, or eccentric orbits,” Teske explained. “If this is the case, it would be an important clue to figuring out the process by which our Solar System formed, and might help us understand where habitable planets are likely to be found.”
The twin stars are named HD 133131A and HD 133131B. The former hosts two Jupiter-sized worlds and the latter a planet with a mass at least 2.5 times Jupiter’s. All three planets have “eccentric” or highly elliptical orbits. So far no smaller, rocky worlds have been detected but the team said those type of planets could be part of the system, or may have been part of the system in the past.
The two stars themselves are separated by only 360 astronomical units (AU – the distance between the Earth and the Sun, approximately 150,000,000 km or 93,000,000 miles). This is extremely close for twin stars with detected planets orbiting the individual stars. The next-closest known binary star system with planets has stars about 1,000 AU apart.
The two stars are more like fraternal twins rather than identical because they have slight different chemical compositions. The team said this could indicate that one star swallowed some baby planets early in its life, changing its composition slightly. Or another option is that the gravitational forces of the detected giant planets may have had a strong effect on fully-formed small planets, flinging them in towards the star or out into space.
But both stars are “metal poor,” meaning that most of their mass is hydrogen and helium, as opposed to other elements like iron or oxygen. This is another curious thing about this system, as most stars that host giant planets are “metal rich.”
The system was found using the Planet Finder Spectrograph, an instrument developed by Carnegie scientists and mounted on the Magellan Clay Telescopes at Carnegie’s Las Campanas Observatory. This finding represents the first exoplanet detection made based solely on data from the. PFS is able to find large planets with long-duration orbits or orbits that are very elliptical rather than circular.
An artist’s depiction of planets transiting a red dwarf star in the TRAPPIST-1 System. Credit: NASA/ESA/STScl
When Hubble first observed the atmospheric conditions of an extrasolar planet in 2000, it opened up that entire field of study. Now, Hubble has conducted the first preliminary study of the atmospheres of Earth-sized, relatively nearby worlds and found “indications that increase the chances of habitability on two exoplanets,” say the researchers.
The planets, TRAPPIST-1b and TRAPPIST-1c, were discovered earlier this year and are approximately 40 light-years away. At the time of their discovery, it was unknown if the worlds were gas planets or rocky worlds, but Hubble’s most recent observations suggest that both planets have compact atmospheres, similar to those of rocky planets such as Earth, Venus, and Mars instead of thick, puffy atmospheres, similar to that of the gas planets like Jupiter.
“Now we can say that these planets are rocky. Now the question is, what kind of atmosphere do they have?” said Julien de Wit of the Massachusetts Institute of Technology, who led a team of scientists to observe the planets in near-infrared light using Hubble’s Wide Field Camera 3. “The plausible scenarios include something like Venus, with high, thick clouds and an atmosphere dominated by carbon dioxide, or an Earth-like atmosphere dominated by nitrogen and oxygen, or even something like Mars with a depleted atmosphere. The next step is to try to disentangle all these possible scenarios that exist for these terrestrial planets.”
Structure of the TRAPPIST-1 exosystem. The green is the star’s habitable zone. Credit: Planetary Habitability Lab.
The exoplanets were originally discovered by the TRAPPIST telescope at ESO’s La Silla observatory in Chile, which, like the Kepler telescope, looks for planetary transits (TRAPPIST stands for Transiting Planets and Planetesimals Small Telescope) observing dips in a star’s light from planets passing in front of it from Earth’s point of view.
The star, TRAPPIST-1, is an ultracool dwarf star and is very small and dim. TRAPPIST-1b completes an orbit around the star in just 1.5 days and TRAPPIST-1c in 2.4 days, and the planets are between 20 and 100 times closer to their star than the Earth is to the sun. Both are tidally locked, where one side of these worlds might be hellish and uninhabitable, but conditions might permit a limited region of habitability on the other side. And because of the star’s faintness, researchers think that TRAPPIST-1c may be within the star’s habitable zone, where moderate temperatures could allow for liquid water to pool.
“A rocky surface is a great start for a habitable planet, but any life on the TRAPPIST-1 planets is likely to have a much harder time than life on Earth,” said Joanna Barstow, an astrophysicist at University College London, who was not involved with the research. “Of course, our ideas of habitability are very narrow because we only have one planet to look at so far, and life might well surprise us by flourishing in what we think of as unlikely conditions.”
The researchers used spectroscopy to decode the light and reveal clues to the chemical makeup of the planets’ atmospheres. While the content of the atmospheres is unknown and are scheduled for more observations, the low concentration of hydrogen and helium has scientists excited about the implications.
The team realized a rare double transit was going to take place, when the two planets would almost simultaneously pass in front of their star, but they only knew two weeks in advance. They took a chance, and taking advantage of Hubble’s ability to do observations on short notice, they wrote up a proposal in a day.
“We thought, maybe we could see if people at Hubble would give us time to do this observation, so we wrote the proposal in less than 24 hours, sent it out, and it was reviewed immediately,” de Wit said. “Now for the first time we have spectroscopic observations of a double transit, which allows us to get insight on the atmosphere of both planets at the same time.”
Using Hubble, the team recorded a combined transmission spectrum of TRAPPIST-1b and c, meaning that as first one planet then the other crossed in front of the star, they were able to measure the changes in wavelength as the amount of starlight dipped with each transit.
“The data turned out to be pristine, absolutely perfect, and the observations were the best that we could have expected,” de Wit says. “The force was certainly with us.”
“These initial Hubble observations are a promising first step in learning more about these nearby worlds, whether they could be rocky like Earth, and whether they could sustain life,” says Geoff Yoder, acting associate administrator for NASA’s Science Mission Directorate in Washington. “This is an exciting time for NASA and exoplanet research.”
Artist's conception of how WISE 0855 might appear if viewed close-up in infrared light. Artwork by Joy Pollard, Gemini Observatory/AURA.
Brown dwarfs – those not-quite-a-planet and not-quite-a-star objects – are intriguing oddities that are too low in mass to burn hydrogen, but are more massive than planets. They only emit a faint amount of light, so they are hard to detect, making scientists unsure of how many of them might be out there in our galaxy.
But astronomers have been keeping an eye one particular brown dwarf known called WISE 0855. Just 7.2 light-years from Earth, it is the coldest known object outside of our Solar System and is just barely visible at infrared wavelengths. But with some crafty spectroscopic observing techniques, astronomers have now determined this object has some exciting characteristics: its atmosphere is full of clouds of water vapor. This is the first time water clouds have been detected outside of our Solar System.
“It’s five times fainter than any other object detected with ground-based spectroscopy at this wavelength,” said Andrew Skemer, assistant professor of astronomy and astrophysics at UC Santa Cruz and the first author on a paper on WISE 0855 published in Astrophysical Journal Letters (paper is available on arXiv here). “Now that we have a spectrum, we can really start thinking about what’s going on in this object. Our spectrum shows that WISE 0855 is dominated by water vapor and clouds, with an overall appearance that is strikingly similar to Jupiter.”
This brown dwarf’s full name is WISE J085510.83-071442.5, but we’re among friends, so it’s W0855 for short. It has about five times the mass of Jupiter and is the coldest brown dwarf ever detected, with an average temperature of about 250 degrees Kelvin, or minus 10 degrees F, minus 20 C. That makes it nearly as cold as Jupiter, which is 130 degrees Kelvin.
“WISE 0855 is our first opportunity to study an extrasolar planetary-mass object that is nearly as cold as our own gas giants,” Skemer said.
Skemer and his team used the Gemini-North telescope in Hawaii and the Gemini Near Infrared Spectrograph to observe WISE 0855 over 13 nights for a total of about 14 hours. Skemer was part of a team that studied this object in 2014 found tentative indications of water clouds based on very limited photometric data. Skemer said obtaining a spectrum (which separates the light from an object into its component wavelengths) was the only way to detect this object’s molecular composition.
A video about the 2014 discovery and study of WISE 0855:
WISE 0855 is too faint for conventional spectroscopy at optical or near-infrared wavelengths, but the team took up a challenge and looked at the thermal emissions from the object at wavelengths in a narrow window around 5 microns.
“I think everyone on the research team really believed that we were dreaming to think we could obtain a spectrum of this brown dwarf because its thermal glow is so feeble,” said Skemer. WISE 0855, is so cool and faint that many astronomers thought it would be years before a spectrum could be obtained. “I thought we’d have to wait until the James Webb Space Telescope was operating to do this,” Skemer said.
This spectroscopic view provided a glimpse into the environment of WISE 0855’s atmosphere. With the data in hand, the researchers then developed atmospheric models of the equilibrium chemistry for a brown dwarf at 250 degrees Kelvin and calculated the resulting spectra under different assumptions, including cloudy and cloud-free models. The models predicted a spectrum dominated by features resulting from water vapor, and the cloudy model yielded the best fit to the features in the spectrum of WISE 0855.
While the spectra of this object are strikingly similar to Jupiter, WISE 0855 appears to have a less turbulent atmosphere.
“The spectrum allows us to investigate dynamical and chemical properties that have long been studied in Jupiter’s atmosphere, but this time on an extrasolar world,” Skemer said.
The scientists say WISE 0855 looks more similar to Jupiter than any exoplanet yet discovered, which is especially intriguing since the Juno mission has just begun its exploration at the giant world. Jupiter, along with the other gas planets in our Solar System, all have clouds and storms, although Jupiter’s clouds are mainly made of ammonia with lower level clouds perhaps containing water. One of Juno’s goals is to determine the global water abundance at Jupiter.
Exoplanet Kepler 62f would need an atmosphere rich in carbon dioxide for water to be in liquid form. Artist's Illustration: NASA Ames/JPL-Caltech/T. Pyle
A team of astronomers suggests that an exoplanet named 62f could be habitable. Kepler data suggests that 62f is likely a rocky planet, and could have oceans. The exoplanet is 40% larger than Earth and is 1200 light years away.
62f is part of a planetary system discovered by the Kepler mission in 2013. There are 5 planets in the system, and they orbit a star that is both cooler and smaller than our Sun. The target of this study, 62f, is the outermost of the planets in the system.
Kepler can’t tell us if a planet is habitable or not. It can only tell us something about its potential habitability. The team, led by Aomawa Shields from the UCLA department of physics and astronomy, used different modeling methods to determine if 62f could be habitable, and the answer is, maybe.
According to the study, much of 62f’s potential habitability revolves around the CO2 component of its atmosphere, if it indeed has an atmosphere. As a greenhouse gas, CO2 can have a significant effect on the temperature of a planet, and hence, a significant effect on its habitability.
Earth’s atmosphere is only 0.04% carbon dioxide (and rising.) 62f would likely need to have much more CO2 than that if it were to support life. It would also require other atmospheric characteristics, .
The study modelled parameters for CO2 concentration, atmospheric density, and orbital characteristics. They simulated:
An atmospheric thickness from the same as Earth’s up to 12 times thicker.
Carbon dioxide concentrations ranging from the same as Earth’s up to 2500 times Earth’s level.
Multiple different orbital configurations.
It may look like the study casts its net pretty wide in order to declare a planet potentially habitable. But the simulations were pretty robust, and relied on more than a single, established modelling method to produce these results. With that in mind, the team found that there are multiple scenarios that could make 62f habitable.
“We found there are multiple atmospheric compositions that allow it to be warm enough to have surface liquid water,” said Shields, a University of California President’s Postdoctoral Program Fellow. “This makes it a strong candidate for a habitable planet.”
Our dear, sweet Earth is the only planet where life is confirmed. Here it is, as seen on July 6, 2015 from a distance of one million miles by a NASA scientific camera aboard the Deep Space Climate Observatory spacecraft. Credits: NASA
As mentioned earlier, CO2 concentration is a big part of it. According to Shields, the planet would need an atmospheric entirely composed of CO2, and an atmosphere five times as dense as Earth’s to be habitable through its entire year. That means that there would be 2500 times more carbon dioxide than Earth has. This would work because the planet’s orbit may take it far enough away from the star for water to freeze, but an atmosphere this dense and this high in CO2 would keep the planet warm.
But there are other conditions that would make 62f habitable, and these include the planet’s orbital characteristics.
“But if it doesn’t have a mechanism to generate lots of carbon dioxide in its atmosphere to keep temperatures warm, and all it had was an Earth-like amount of carbon dioxide, certain orbital configurations could allow Kepler-62f’s surface temperatures to temporarily get above freezing during a portion of its year,” said Shields. “And this might help melt ice sheets formed at other times in the planet’s orbit.”
Shields and her team used multiple modelling methods to produce these results. The climate was modelled using the Community Climate System Model and the Laboratoire de Me´te´orologie Dynamique Generic model. The planet’s orbital characteristics were modelled using HNBody. This study represents the first time that these modelling methods were combined, and this combined method can be used on other planets.
Shields said, “This will help us understand how likely certain planets are to be habitable over a wide range of factors, for which we don’t yet have data from telescopes. And it will allow us to generate a prioritized list of targets to follow up on more closely with the next generation of telescopes that can look for the atmospheric fingerprints of life on another world.”
There are over 2300 confirmed exoplanets, and many more candidates yet to be confirmed. Only a handful of them have been confirmed as being in the habitable zone around their host star. Of course, we don’t know if life can exist on other planets, even if they do reproduce the same kind of habitability that Earth has. We just have no way of knowing, yet.
That will change when instruments like the James Webb Space Telescope are able to peer into the atmospheres of exoplanets and tell us something about any bio-markers that might be present.
But until then, and until we actually visit another world with a probe of some design, we need to use modelling like the type employed in this study, to get us closer to answering the question of life on other worlds.
Artist's concept of the prototype starshade, a giant structure designed to block the glare of stars so that future space telescopes can take pictures of planets. Credit: NASA/JPL
For countless generations, people have looked up at the stars and wondered if life exists somewhere out there, perhaps on planets much like ours. But it has only been in recent decades that we have been able to confirm the existence of extrasolar planets (aka. exoplanets) in other star systems. In fact, between 1988 and April 20th of 2016, astronomers have been able to account for the existence of 2108 planets in 1350 different star systems, including 511 multiple planetary systems.
Most of these discoveries have taken place within just the past three years, thanks to improvements in our detection methods, and the deployment of the Kepler space observatory in 2009. Looking ahead, astronomers hope to improve on these methods even further with the introduction of the Starshade, a giant space structure designed to block the glare of stars, thus making it easier to find planets – and perhaps another Earth!
The Wild Duck Cluster photographed on amateur astrophotography equipment. Credit: Creative Commons/Rawastrodata
Welcome back to another edition of Messier Monday! Today, we continue in our tribute to Tammy Plotner with a look at the M11 Wild Duck Cluster!
In the 18th century, French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky while searching for comets. Hoping to ensure that other astronomers did not make the same mistake, he began compiling a list of 1oo of them. This list came to be known as the Messier Catalog, and would have far-reaching consequences.
One of these objects is M11, otherwise known as The Wild Duck Cluster, an open cluster located in the constellation Scutum, near the northern edge of a rich Milky Way star cloud (the Scutum Cloud). This open star cluster is one of the richest and most compact of all those known, composed of a few thousand hot, young stars that are only a few million years old.
Artist's impression of the terraforming of Mars, from its current state to a livable world. Credit: Daein Ballard
Terraforming. Chances are you’ve heard that word uttered before, most likely in the context of some science fiction story. However, in recent years, thanks to renewed interest in space exploration, this word is being used in an increasingly serious manner. And rather than being talked about like a far-off prospect, the issue of terraforming other worlds is being addressed as a near-future possibility.
In recent years, we’ve heard luminaries like Elon Musk and Stephen Hawking claiming that humanity needs a “backup location” to ensure our survival, private ventures like Mars One enlisting thousands of volunteers to colonize the Red Planet, and space agencies like NASA, the ESA, and China discussing the prospect of long-term habitability on Mars or the Moon. From all indications, it looks like terraforming is yet another science-fiction concept that is migrating into the realm of science fact.
But just what does terraforming entail? Where exactly could we go about using this process? What kind of technology would we need? Does such technology already exist, or do we have to wait? How much in the way of resources would it take? And above all, what are the odds of it succeeding? Answering any or all of these questions requires a bit of digging. Not only is terraforming a time-honored concept, but as it turns out, humanity already has quite a bit of experience in this area!
Origin Of The Term:
To break it down, terraforming is the process whereby a hostile environment (i.e., a planet that is too cold, too hot, and/or has an unbreathable atmosphere) is altered to make it suitable for human life. This could involve modifying the temperature, atmosphere, surface topography, ecology, or all of the above to make a planet or moon more “Earth-like.”
Venus is considered by many to be a prime candidate for terraforming. Credit: NASA/JPL/io9.com
The term was coined by Jack Williamson, an American science fiction writer who has also been called “the Dean of science fiction” (after the death of Robert Heinlein in 1988). The term appeared as part of a science-fiction story, titled “Collision Orbit,” published in the 1942 edition of the magazineAstounding Science Fiction. This is the first known mention of the concept, though there are examples of it appearing in fiction beforehand.
Terraforming in Fiction:
Science fiction is filled with examples of altering planetary environments to be more suitable to human life, many of which predate scientific studies by many decades. For example, in H.G. Wells’ War of the Worlds, he mentions at one point how the Martian invaders begin transforming Earth’s ecology for the sake of long-term habitation.
In Olaf Stapleton’s Last And First Men(1930), two chapters are dedicated to describing how humanity’s descendants terraform Venus after Earth becomes uninhabitable. In the process, they commit genocide against the native aquatic life. By the 1950s and 60s, due to the beginning of the Space Age, terraforming appeared in works of science fiction with increasing frequency.
One such example is Farmer in the Sky (1950) by Robert A. Heinlein. In this novel, Heinlein offers a vision of Jupiter’s moon Ganymede that is being transformed into an agricultural settlement. This was a very significant work, in that it was the first where the concept of terraforming is presented as a serious and scientific matter, rather than the subject of mere fantasy.
Scene from 2010: The Year We Make Contact, the movie adaptation of Clarke’s novel. Credit: Metro-Goldwyn-Mayer
In 1951, Arthur C. Clarke wrote the first novel in which the terraforming of Mars was presented in fiction. Titled The Sands of Mars, the story involves Martian settlers heating up the planet by converting Mars’ moon Phobos into a second sun and growing plants that break down the Martian sands in order to release oxygen. In his seminal book 2001: A Space Odyssey – and its sequel,2010: Odyssey Two – Clarke presents a race of ancient beings (“Firstborn”) turning Jupiter into a second sun so that Europa will become a life-bearing planet.
Poul Anderson also wrote extensively about terraforming in the 1950s. In his 1954 novel, The Big Rain, Venus is altered through planetary engineering techniques over a very long period of time. The book was so influential that the term term “Big Rain” has since come to be synonymous with the terraforming of Venus. This was followed in 1958 by the Snows of Ganymede, where the Jovian moon’s ecology is made habitable through a similar process.
In Issac Asimov’s Robot series, colonization and terraforming are performed by a powerful race of humans known as “Spacers,” who conduct this process on fifty planets in the known universe. In his Foundation series, humanity has effectively colonized every habitable planet in the galaxy and terraformed them to become part of the Galactic Empire.
In 1984, James Lovelock and Michael Allaby wrote what is considered by many to be one of the most influential books on terraforming. Titled The Greening of Mars, the novel explores the formation and evolution of planets, the origin of life, and Earth’s biosphere. The terraforming models presented in the book actually foreshadowed future debates regarding the goals of terraforming.
Kim Stanley Robinson’s Red Mars Trilogy. Credit: variety.com
In the 1990s, Kim Stanley Robinson released his famous trilogy that deals with the terraforming of Mars. Known as the Mars Trilogy – Red Mars, Green Mars, Blue Mars – this series centers on the transformation of Mars over the course of many generations into a thriving human civilization. This was followed up in 2012 with the release of 2312, which deals with the colonization of the Solar System – including the terraforming of Venus and other planets.
Countless other examples can be found in popular culture, ranging from television and print to films and video games.
Study of Terraforming:
In an article published by the journal Science in 1961, famed astronomer Carl Sagan proposed using planetary engineering techniques to transform Venus. This involved seeding the atmosphere of Venus with algae, which would convert the atmosphere’s ample supplies of water, nitrogen, and carbon dioxide into organic compounds and reduce Venus’ runaway greenhouse effect.
In 1973, he published an article in the journal Icarus titled “Planetary Engineering on Mars,” where he proposed two scenarios for transforming Mars. These included transporting low albedo material and/or planting dark plants on the polar ice caps to ensure it absorbed more heat, melted, and converted the planet to more “Earth-like conditions.”
In 1976, NASA addressed the issue of planetary engineering officially in a study titled “On the Habitability of Mars: An Approach to Planetary Ecosynthesis.” The study concluded that photosynthetic organisms, the melting of the polar ice caps, and the introduction of greenhouse gases could all be used to create a warmer, oxygen, and ozone-rich atmosphere. The first conference session on terraforming – referred to as “Planetary Modeling” at the time- was organized that same year.
Artist concept of a ‘Living’ Mars. Credit: Kevin Gill
And then in March of 1979, NASA engineer and author James Oberg organized the First Terraforming Colloquium – a special session at the Tenth Lunar and Planetary Science Conference, which is held annually in Houston, Texas. In 1981, Oberg popularized the concepts that were discussed at the colloquium in his book New Earths: Restructuring Earth and Other Planets.
In 1982, Planetologist Christopher McKay wrote “Terraforming Mars”, a paper for the Journal of the British Interplanetary Society. In it, McKay discussed the prospects of a self-regulating Martian biosphere, which included both the required methods for doing so and the ethics of it. This was the first time that the word terraforming was used in the title of a published article, and would henceforth become the preferred term.
This was followed by James Lovelock and Michael Allaby’s The Greening of Mars in 1984. This book was one of the first to describe a novel method of warming Mars, where chlorofluorocarbons (CFCs) are added to the atmosphere in order to trigger global warming. This book motivated biophysicist Robert Haynes to begin promoting terraforming as part of a larger concept known as Ecopoiesis.
Derived from the Greek words oikos (“house”) and poiesis (“production”), this word refers to the origin of an ecosystem. In the context of space exploration, it involves a form of planetary engineering where a sustainable ecosystem is fabricated from an otherwise sterile planet. As described by Haynes, this begins with the seeding of a planet with microbial life, which leads to conditions approaching that of a primordial Earth. This is then followed by the importation of plant life, which accelerates the production of oxygen, and culminates in the introduction of animal life.
An engineer suggests building a roof over a small planet so that Earth-like conditions could be maintained. Credit: Karl Tate/space.com
There is also the concept where a usable part of a planet is enclosed in a dome in order to transform its environment, which is known as “paraterraforming”. This concept, originally coined by British mathematician Richard L.S. Talyor in his 1992 publication Paraterraforming – The worldhouse concept, could be used to terraform sections of several planets that are otherwise inhospitable, or cannot be altered in whole.
Potential Sites:
Within the Solar System, several possible locations exist that could be well-suited to terraforming. Consider the fact that besides Earth, Venus and Mars also lie within the Sun’s Habitable Zone (aka. “Goldilocks Zone”). However, owing to Venus’ runaway greenhouse effect, and Mars’ lack of a magnetosphere, their atmospheres are either too thick and hot or too thin and cold, to sustain life as we know it. However, this could theoretically be altered through the right kind of ecological engineering.
Other potential sites in the Solar System include some of the moons that orbit the gas giants. Several Jovian (i.e. in orbit of Jupiter) and Cronian (in orbit of Saturn) moons have an abundance of water ice, and scientists have speculated that if the surface temperatures were increased, viable atmospheres could be created through electrolysis and the introduction of buffer gases.
Artist’s conception of a terraformed Mars. Credit: Ittiz/Wikimedia Commons
There is even speculation that Mercury and the Moon (or at least parts thereof) could be terraformed in order to be suitable for human settlement. In these cases, terraforming would require not only altering the surface but perhaps also adjusting their rotation. In the end, each case presents its own share of advantages, challenges, and likelihoods for success. Let’s consider them in order of distance from the Sun.
Inner Solar System:
The terrestrial planets of our Solar System present the best possibilities for terraforming. Not only are they located closer to our Sun, and thus in a better position to absorb its energy, but they are also rich in silicates and minerals – which any future colonies will need to grow food and build settlements. And as already mentioned, two of these planets (Venus and Mars) skirt the inner and outer edge of the Sun’s habitable zone.
Mercury: The vast majority of Mercury’s surface is hostile to life, where temperatures gravitate between extremely hot and cold – i.e. 700 K (427 °C; 800 °F) 100 K (-173 °C; -280 °F). This is due to its proximity to the Sun, the almost total lack of an atmosphere, and its very slow rotation. However, at the poles, temperatures are consistently low -93 °C (-135 °F) due to it being permanently shadowed.
Images of Mercury’s northern polar region, provided by MESSENGER. Credit: NASA/JPL
The presence of water ice and organic molecules in the northern polar region has also been confirmed thanks to data obtained by the MESSENGER mission. Colonies could therefore be constructed in the regions, and limited terraforming (aka. paraterraforming) could take place. For example, if domes (or a single dome) of sufficient size could be built over the Kandinsky, Prokofiev, Tolkien, and Tryggvadottir craters, the northern region could be altered for human habitation.
Theoretically, this could be done by using mirrors to redirect sunlight into the domes which would gradually raise the temperature. The water ice would then melt, and when combined with organic molecules and finely ground sand, soil could be made. Plants could then be grown to produce oxygen, which combined with nitrogen gas, would produce a breathable atmosphere.
Venus: As “Earth’s Twin“, there are many possibilities and advantages to terraforming Venus. The first to propose this was Sagan with his 1961 article in Science. However, subsequent discoveries – such as the high concentrations of sulfuric acid in Venus’ clouds – made this idea unfeasible. Even if algae could survive in such an atmosphere, converting the extremely dense clouds of CO² into oxygen would result in an over-dense oxygen environment.
In addition, graphite would become a by-product of the chemical reactions, which would likely form into a thick powder on the surface. This would become CO² again through combustion, thus restarting the entire greenhouse effect. However, more recent proposals have been made that advocate using carbon sequestration techniques, which are arguably much more practical.
In these scenarios, chemical reactions would be relied on to convert Venus’ atmosphere to something breathable while also reducing its density. In one scenario, hydrogen and iron aerosol would be introduced to convert the CO² in the atmosphere into graphite and water. This water would then fall to the surface, where it will cover roughly 80% of the planet – due to Venus having little variation in elevation.
Another scenario calls for the introduction of vast amounts of calcium and magnesium into the atmosphere. This would sequester carbon in the form of calcium and magnesium carbonates. An advantage to this plan is that Venus already has deposits of both minerals in its mantle, which could then be exposed to the atmosphere through drilling. However, most of the minerals would have to come from off-world in order to reduce the temperature and pressure to sustainable levels.
Yet another proposal is to freeze the atmospheric carbon dioxide down to the point of liquefaction – where it forms dry ice – and letting it accumulate on the surface. Once there, it could be buried and would remain in a solid state due to pressure, and even mined for local and off-world use. And then there is the possibility of bombarding the surface with icy comets (which could be mined from one of Jupiter’s or Saturn’s moons) to create a liquid ocean on the surface, which would sequester carbon and aid in any other of the above processes.
Last, there is the scenario in which Venus’ dense atmosphere could be removed. This could be characterized as the most direct approach to thinning an atmosphere that is far too dense for human occupation. By colliding large comets or asteroids into the surface, some of the dense CO² clouds could be blasted into space, thus leaving less atmosphere to be converted.
Artist’s conception of a terraformed Venus, showing a surface largely covered in oceans. Credit: Wikipedia Commons/Ittiz
A slower method could be achieved using mass drivers (aka. electromagnetic catapults) or space elevators, which would gradually scoop up the atmosphere and either lift it into space or fire it away from the surface. And beyond altering or removing the atmosphere, there are also concepts that call for reducing the heat and pressure by either limiting sunlight (i.e. with solar shades) or altering the planet’s rotational velocity.
The concept of solar shades involves using either a series of small spacecraft or a single large lens to divert sunlight from a planet’s surface, thus reducing global temperatures. For Venus, which absorbs twice as much sunlight as Earth, solar radiation is believed to have played a major role in the runaway greenhouse effect that has made it what it is today.
Such a shade could be space-based, located in the Sun-Venus L1 Lagrangian Point, where it would not only prevent some sunlight from reaching Venus but also serve to reduce the amount of radiation Venus is exposed to. Alternately, solar shades or reflectors could be placed in the atmosphere or on the surface. This could consist of large reflective balloons, sheets of carbon nanotubes or graphene, or low-albedo material.
Placing shades or reflectors in the atmosphere offers two advantages: for one, atmospheric reflectors could be built in-situ, using locally-sourced carbon. Second, Venus’ atmosphere is dense enough that such structures could easily float atop the clouds. However, the amount of material would have to be large and would have to remain in place long after the atmosphere had been modified. Also, since Venus already has highly reflective clouds, any approach would have to significantly surpass its current albedo (0.65) to make a difference.
Solar shades placed in orbit of Venus are a possible means of terraforming the planet. Credit: IEEE Spectrum/John MacNeill
Also, the idea of speeding up Venus’ rotation has been floating around as a possible means of terraforming. If Venus could be spun-up to the point where its diurnal (day-night) cycle is similar to Earth’s, the planet might just begin to generate a stronger magnetic field. This would have the effect of reducing the amount of solar wind (and hence radiation) from reaching the surface, thus making it safer for terrestrial organisms.
The Moon: As Earth’s closest celestial body, colonizing the Moon would be comparatively easy compared to other bodies. But when it comes to terraforming the Moon, the possibilities and challenges closely resemble those of Mercury. For starters, the Moon has an atmosphere that is so thin that it can only be referred to as an exosphere. What’s more, the volatile elements that are necessary for life are in short supply (i.e. hydrogen, nitrogen, and carbon).
These problems could be addressed by capturing comets that contain water ices and volatiles and crashing them into the surface. The comets would sublimate, dispersing these gases and water vapor to create an atmosphere. These impacts would also liberate water that is contained in the lunar regolith, which could eventually accumulate on the surface to form natural bodies of water.
The transfer of momentum from these comets would also get the Moon rotating more rapidly, speeding up its rotation so that it would no longer be tidally locked. A Moon that was sped up to rotate once on its axis every 24 hours would have a steady diurnal cycle, which would make colonization and adapting to life on the Moon easier.
There is also the possibility of paraterraforming parts of the Moon in a way that would be similar to terraforming Mercury’s polar region. In the Moon’s case, this would take place in the Shackleton Crater, where scientists have already found evidence of water ice. Using solar mirrors and a dome, this crater could be turned into a micro-climate where plants could be grown and a breathable atmosphere created.
Mars: When it comes to terraforming, Mars is the most popular destination. There are several reasons for this, ranging from its proximity to Earth, its similarities to Earth, and the fact that it once had an environment that was very similar to Earth’s – which included a thicker atmosphere and the presence of warm, flowing water on the surface. Lastly, it is currently believed that Mars may have additional sources of water beneath its surface.
In brief, Mars has a diurnal and seasonal cycle that are very close to what we experience here on Earth. In the former case, a single day on Mars lasts 24 hours and 40 minutes. In the latter case, and owing to Mars’ similarly-tilted axis (25.19° compared to Earth’s 23°), Mars experiences seasonal changes that are very similar to Earth’s. Though a single season on Mars lasts roughly twice as long, the temperature variation that results is very similar – ±178 °C (320°F) compared to Earth’s ±160 °C (278°F).
Beyond these, Mars would need to undergo vast transformations in order for human beings to live on its surface. The atmosphere would need to be thickened drastically, and its composition would need to be changed. Currently, Mars’ atmosphere is composed of 96% carbon dioxide, 1.93% argon, and 1.89% nitrogen, and the air pressure is equivalent to only 1% of Earth’s at sea level.
Above all, Mars lacks a magnetosphere, which means that its surface receives significantly more radiation than we are used to here on Earth. In addition, it is believed that Mars once had a magnetosphere and that the disappearance of this magnetic field led to the stripping of Mars’ atmosphere by solar wind. This in turn is what led Mars to become the cold, desiccated place it is today.
Scientists were able to gauge the rate of water loss on Mars by measuring the ratio of water and HDO from today and 4.3 billion years ago. Credit: Kevin Gill
Ultimately, this means that in order for the planet to become habitable by human standards, its atmosphere would need to be significantly thickened and the planet significantly warmed. The composition of the atmosphere would need to change as well, from the current CO²-heavy mix to a nitrogen-oxygen balance of about 70/30. And above all, the atmosphere would need to be replenished every so often to compensate for the loss.
Luckily, the first three requirements are largely complementary, and present a wide range of possible solutions. For starters, Mars’ atmosphere could be thickened and the planet warmed by bombarding its polar regions with meteors. These would cause the poles to melt, releasing their deposits of frozen carbon dioxide and water into the atmosphere and triggering a greenhouse effect.
The introduction of volatile elements, such as ammonia and methane, would also help to thicken the atmosphere and trigger warming. Both could be mined from the icy moons of the outer Solar System, particularly from the moons of Ganymede, Callisto, and Titan. These could also be delivered to the surface via meteoric impacts.
After impacting on the surface, the ammonia ice would sublimate and break down into hydrogen and nitrogen – the hydrogen interacting with the CO² to form water and graphite, while the nitrogen acts as a buffer gas. The methane, meanwhile, would act as a greenhouse gas that would further enhance global warming. In addition, the impacts would throw tons of dust into the air, further fueling the warming trend.
In time, Mars’ ample supplies of water ice – which can be found not only in the poles but in vast subsurface deposits of permafrost – would all sublimate to form warm, flowing water. And with significantly increased air pressure and a warmer atmosphere, humans might be able to venture out onto the surface without the need for pressure suits.
However, the atmosphere will still need to be converted into something breathable. This will be far more time-consuming, as the process of converting the atmospheric CO² into oxygen gas will likely take centuries. In any case, several possibilities have been suggested, which include converting the atmosphere through photosynthesis – either with cyanobacteria or Earth plants and lichens.
Other suggestions include building orbital mirrors, which would be placed near the poles and direct sunlight onto the surface to trigger a cycle of warming by causing the polar ice caps to melt and release their CO² gas. Using dark dust from Phobos and Deimos to reduce the surface’s albedo, thus allowing it to absorb more sunlight, has also been suggested.
In short, there are plenty of options for terraforming Mars. And many of them, if not being readily available, are at least on the table…
Outer Solar System:
Beyond the Inner Solar System, there are several sites that would make for good terraforming targets as well. Particularly around Jupiter and Saturn, there are several sizable moons – some of which are larger than Mercury – that have an abundance of water in the form of ice (and in some cases, maybe even interior oceans).
The moons of the Solar System, shown to scale. Credit: planetary.org
At the same time, many of these same moons contain other necessary ingredients for functioning ecosystems, such as frozen volatiles – like ammonia and methane. Because of this, and as part of our ongoing desire to explore farther out into our Solar System, many proposals have been made to seed these moons with bases and research stations. Some plans even include possible terraforming to make them suitable for long-term habitation.
The Jovian Moons: Jupiter’s largest moons, Io, Europa, Ganymede, and Callisto – known as the Galileans, after their founder (Galileo Galilei) – have long been the subject of scientific interest. For decades, scientists have speculated about the possible existence of a subsurface ocean on Europa, based on theories about the planet’s tidal heating (a consequence of its eccentric orbit and orbital resonance with the other moons).
Analysis of images provided by the Voyager 1and Galileo probes added weight to this theory, showing regions where it appeared that the subsurface ocean had melted through. What’s more, the presence of this warm water ocean has also led to speculation about the existence of life beneath Europa’s icy crust – possibly around hydrothermal vents at the core-mantle boundary.
Because of this potential for habitability, Europa has also been suggested as a possible site for terraforming. As the argument goes, if the surface temperature could be increased, and the surface ice melted, the entire planet could become an ocean world. Sublimation of the ice, which would release water vapor and gaseous volatiles, would then be subject to electrolysis (which already produces a thin oxygen atmosphere).
However, Europa has no magnetosphere of its own and lies within Jupiter’s powerful magnetic field. As a result, its surface is exposed to significant amounts of radiation – 540 rem of radiation per day compared to about 0.0030 rem per year here on Earth – and any atmosphere we create would begin to be stripped away by Jupiter. Ergo, radiation shielding would need to be put in place that could deflect the majority of this radiation.
And then there is Ganymede, the third most-distant of Jupiter’s Galilean moons. Much like Europa, it is a potential site of terraforming and presents numerous advantages. For one, it is the largest moon in our Solar System, larger than our own moon and even larger than the planet Mercury. In addition, it also has ample supplies of water ice, is believed to have an interior ocean, and even has its own magnetosphere.
Hence, if the surface temperature were increased and the ice sublimated, Ganymede’s atmosphere could be thickened. Like Europa, it would also become an ocean planet, and its own magnetosphere would allow for it to hold on to more of its atmosphere. However, Jupiter’s magnetic field still exerts a powerful influence over the planet, which means radiation shields would still be needed.
Lastly, there is Callisto, the fourth-most distant of the Galileans. Here too, abundant supplies of water ice, volatiles, and the possibility of an interior ocean all point towards the potential for habitability. But in Callisto’s case, there is the added bonus of it being beyond Jupiter’s magnetic field, which reduces the threat of radiation and atmospheric loss.
Artist’s cut-away representation of the internal structure of Ganymede. Credit: Wikipedia Commons/kelvinsong
The process would begin with surface heating, which would sublimate the water ice and Callisto’s supplies of frozen ammonia. From these oceans, electrolysis would lead to the formation of an oxygen-rich atmosphere, and the ammonia could be converted into nitrogen to act as a buffer gas. However, since the majority of Callisto is ice, it would mean that the planet would lose considerable mass and have no continents. Again, an ocean planet would result, necessitating floating cities or massive colony ships.
The Cronians Moons: Much like the Jovian Moons, Saturn’s Moons (also known as the Cronian) present opportunities for terraforming. Again, this is due to the presence of water ice, interior oceans, and volatile elements. Titan, Saturn’s largest moon, also has an abundance of methane that comes in liquid form (the methane lakes around its northern polar region) and in gaseous form in its atmosphere. Large caches of ammonia are also believed to exist beneath the surface ice.
Titan is also the only natural satellite to have a dense atmosphere (one and half times the pressure of Earth’s) and the only planet outside of Earth where the atmosphere is nitrogen-rich. Such a thick atmosphere would mean that it would be far easier to equalize pressure for habitats on the planet. What’s more, scientists believe this atmosphere is a prebiotic environment rich in organic chemistry – i.e. similar to Earth’s early atmosphere (only much colder).
Diagram of the internal structure of Titan according to the fully differentiated dense-ocean model. Credit: Wikipedia Commons/Kelvinsong
As such, converting it to something Earth-like would be feasible. First, the surface temperature would need to be increased. Since Titan is very distant from the Sun and already has an abundance of greenhouse gases, this could only be accomplished through orbital mirrors. This would sublimate the surface ice, releasing ammonia beneath, which would lead to more heating.
The next step would involve converting the atmosphere to something breathable. As already noted, Titan’s atmosphere is nitrogen-rich, which would remove the need for introducing a buffer gas. And with the availability of water, oxygen could be introduced by generating it through electrolysis. At the same time, the methane and other hydrocarbons would have to be sequestered, in order to prevent an explosive mixture with the oxygen.
But given the thickness and multi-layered nature of Titan’s ice, which is estimated to account for half of its mass, the moon would be very much an ocean planet- i.e. with no continents or landmasses to build on. So once again, any habitats would have to take the form of either floating platforms or large ships.
Enceladus is another possibility, thanks to the recent discovery of a subsurface ocean. Analysis by the Cassini space probe of the water plumes erupting from its southern polar region also indicated the presence of organic molecules. As such, terraforming it would be similar to terraforming Jupiter’s moon of Europa, and would yield a similar ocean moon.
Artist’s rendering of possible hydrothermal activity that may be taking place on and under the seafloor of Enceladus. Credit: NASA/JPL
Again, this would likely have to involve orbital mirrors, given Enceladus’ distance from our Sun. Once the ice began to sublimate, electrolysis would generate oxygen gas. The presence of ammonia in the subsurface ocean would also be released, helping to raise the temperature and serving as a source of nitrogen gas, with which to buffer the atmosphere.
Exoplanets: In addition to the Solar System, extra-solar planets (aka. exoplanets) are also potential sites for terraforming. Of the 1,941 confirmed exoplanets discovered so far, these planets are those that have been designated “Earth-like. In other words, they are terrestrial planets that have atmospheres and, like Earth, occupy the region around a star where the average surface temperature allows for liquid water (aka. habitable zone).
The first planet confirmed by Kepler to have an average orbital distance that placed it within its star’s habitable zone was Kepler-22b. This planet is located about 600 light-years from Earth in the constellation of Cygnus, was first observed on May 12th, 2009, and then confirmed on Dec 5th, 2011. Based on all the data obtained, scientists believe that this world is roughly 2.4 times the radius of Earth, and is likely covered in oceans or has a liquid or gaseous outer shell.
In addition, there are star systems with multiple “Earth-like” planets occupying their habitable zones. Gliese 581 is a good example, a red dwarf star that is located 20.22 light-years away from Earth in the Libra constellation. Here, three confirmed and two possible planets exist, two of which are believed to orbit within the star’s habitable zone. These include the confirmed planet Gliese 581 d and the hypothetical Gliese 581 g.
Tau Ceti is another example. This G-class star, which is located roughly 12 light-years from Earth in the constellation Cetus, has five possible planets orbiting it. Two of these are Super-Earths that are believed to orbit the star’s habitable zone – Tau Ceti e and Tau Ceti f. However, Tau Ceti e is believed to be too close for anything other than Venus-like conditions to exist on its surface.
In all cases, terraforming the atmospheres of these planets would most likely involve the same techniques used to terraform Venus and Mars, though to varying degrees. For those located on the outer edge of their habitable zones, terraforming could be accomplished by introducing greenhouse gases or covering the surface with low albedo material to trigger global warming. On the other end, solar shades and carbon sequestering techniques could reduce temperatures to the point where the planet is considered hospitable.
The latest list of potentially habitable exoplanets, courtesy of The Planetary Habitability Laboratory. Credit: phl.upr.edu
Potential Benefits:
When addressing the issue of terraforming, there is the inevitable question – “why should we?” Given the expenditure in resources, the time involved, and other challenges that naturally arise (see below), what reasons are there to engage in terraforming? As already mentioned, there are the reasons cited by Musk, about the need to have a “backup location” to prevent any particular cataclysm from claiming all of humanity.
Putting aside for the moment the prospect of a nuclear holocaust, there is also the likelihood that life will become untenable on certain parts of our planet in the coming century. As the NOAA reported in March of 2015, carbon dioxide levels in the atmosphere have now surpassed 400 ppm, a level not seen since the Pliocene Era – when global temperatures and sea levels were significantly higher.
And as a series of scenarios computed by NASA show, this trend is likely to continue until 2100, and with serious consequences. In one scenario, carbon dioxide emissions will level off at about 550 ppm toward the end of the century, resulting in an average temperature increase of 2.5 °C (4.5 °F). In the second scenario, carbon dioxide emissions rise to about 800 ppm, resulting in an average increase of about 4.5 °C (8 °F). Whereas the increases predicted in the first scenario are sustainable, in the latter scenario, life will become untenable on many parts of the planet.
NASA predicts that, based on current emissions rates, temperatures could increase by up to 4.5 degrees Celsius by 2100. Credit: svs.gsfc.nasa.gov
As a result of this, creating a long-term home for humanity on Mars, the Moon, Venus, or elsewhere in the Solar System may be necessary. In addition to offering us other locations from which to extract resources, cultivate food, and as a possible outlet for population pressures, having colonies on other worlds could mean the difference between long-term survival and extinction.
There is also the argument that humanity is already well-versed in altering planetary environments. For centuries, humanity’s reliance on industrial machinery, coal, and fossil fuels has had a measurable effect on Earth’s environment. And whereas the Greenhouse Effect that we have triggered here was not deliberate, our experience and knowledge in creating it here on Earth could be put to good use on planets where surface temperatures need to be raised artificially.
In addition, it has also been argued that working with environments where there is a runaway Greenhouse Effect – i.e. Venus – could yield valuable knowledge that could in turn be used here on Earth. Whether it is the use of extreme bacteria, introducing new gases, or mineral elements to sequester carbon, testing these methods out on Venus could help us to combat Climate Change here at home.
It has also been argued that Mars’ similarities to Earth are a good reason to terraform it. Essentially, Mars once resembled Earth, until its atmosphere was stripped away, causing it to lose virtually all the liquid water on its surface. Ergo, terraforming it would be tantamount to returning it to its once-warm and watery glory. The same argument could be made of Venus, where efforts to alter it would restore it to what it was before a runaway Greenhouse Effect turned it into the harsh, extremely hot world it is today.
Artist’s concept for a SpaceX Mars Colonization Transport (MCT). (Credit: Reddit user P3rkoz)
Last, but not least, there is the argument that colonizing the Solar System could usher in an age of “post-scarcity”. If humanity were to build outposts and based on other worlds, mine the asteroid belt, and harvest the resources of the Outer Solar System, we would effectively have enough minerals, gases, energy, and water resources to last us indefinitely. It could also help trigger a massive acceleration in human development, defined by leaps and bounds in technological and social progress.
Potential Challenges:
When it comes right down to it, all of the scenarios listed above suffer from one or more of the following problems:
They are not possible with existing technology
They require a massive commitment of resources
They solve one problem, only to create another
They do not offer a significant return on the investment
They would take a really, REALLY long time
Case in point, all of the potential ideas for terraforming Venus and Mars involve infrastructure that does not yet exist and would be very expensive to create. For instance, the orbital shade concept that would cool Venus calls for a structure that would need to be four times the diameter of Venus itself (if it were positioned at L1). It would therefore require megatons of material, all of which would have to be assembled on site.
All asteroids and comets visited by spacecraft as of November 2010. Credits: Emily Lakdawalla/NASA/JPL/Ted Stryk/ESA/OSIRIS team/JHUAPL/ISAS/JAXA/RAS/UMD
In contrast, increasing the speed of Venus’s rotation would require energy many orders of magnitude greater than the construction of orbiting solar mirrors. As with removing Venus’ atmosphere, the process would also require a significant number of impactors that would have to be harnessed from the outer solar System – mainly from the Kuiper Belt.
In order to do this, a large fleet of spaceships would be needed to haul them, and they would need to be equipped with advanced drive systems that could make the trip in a reasonable amount of time. Currently, no such drive systems exist, and conventional methods – ranging from ion engines to chemical propellants – are neither fast or economical enough.
To illustrate, NASA’s New Horizons mission took more than 11 years to get make its historic rendezvous with Pluto in the Kuiper Belt, using conventional rockets and the gravity-assist method. Meanwhile, the Dawn mission, which relied on ionic propulsion, took almost four years to reach Vesta in the Asteroid Belt. Neither method is practical for making repeated trips to the Kuiper Belt and hauling back icy comets and asteroids, and humanity has nowhere near the number of ships we would need to do this.
The Moon’s proximity makes it an attractive option for terraforming. But again, the resources needed – which would likely include several hundred comets – would again need to be imported from the outer Solar System. And while Mercury’s resources could be harvested in-situ or brought from Earth to paraterraform its northern polar region, the concept still calls for a large fleet of ships and robot builders which do not yet exist.
The moons of Saturn, from left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top) and Hyperion (bottom). Credit: NASA/JPL/Space Science Institute
The outer Solar System presents a similar problem. In order to begin terraforming these moons, we would need infrastructure between here and there, which would mean bases on the Moon, Mars, and within the Asteroid Belt. Here, ships could refuel as they transport materials to the Jovian sand Cronian systems, and resources could be harvested from all three of these locations as well as within the systems themselves.
But of course, it would take many, many generations (or even centuries) to build all of that, and at considerable cost. Ergo, any attempts at terraforming the outer Solar System would have to wait until humanity had effectively colonized the inner Solar System. And terraforming the Inner Solar System will not be possible until humanity has plenty of space hauler on hand, not to mention fast ones!
The necessity for radiation shields also presents a problem. The size and cost of manufacturing shields that could deflect Jupiter’s magnetic field would be astronomical. And while the resources could be harvested from the nearby Asteroid Belt, transporting and assembling them in space around the Jovian Moons would again require many ships and robotic workers. And again, there would have to be extensive infrastructure between Earth and the Jovian system before any of this could proceed.
As for item three, there are plenty of problems that could result from terraforming. For instance, transforming Jupiter’s and Saturn’s moons into ocean worlds could be pointless, as the volume of liquid water would constitute a major portion of the moon’s overall radius. Combined with their low surface gravities, high orbital velocities, and the tidal effects of their parent planets, this could lead to severely high waves on their surfaces. In fact, these moons could become totally unstable as a result of being altered.
Mars-manned-mission vehicle (NASA Human Exploration of Mars Design Reference Architecture 5.0) Feb. 2009. Credit: NASA
There are also several questions about the ethics of terraforming. Basically, altering other planets in order to make them more suitable to human needs raises the natural question of what would happen to any lifeforms already living there. If in fact Mars and other Solar System bodies have indigenous microbial (or more complex) life, which many scientists suspect, then altering their ecology could impact or even wipe out these lifeforms. In short, future colonists and terrestrial engineers would effectively be committing genocide.
Another argument that is often made against terraforming is that any effort to alter the ecology of another planet does not present any immediate benefits. Given the cost involved, what possible incentive is there to commit so much time, resources, and energy to such a project? While the idea of utilizing the resources of the Solar System makes sense in the long run, the short-term gains are far less tangible.
Basically, harvested resources from other worlds is not economically viable when you can extract them here at home for much less. And real-estate is only the basis of an economic model if the real estate itself is desirable. While MarsOne has certainly shown us that there are plenty of human beings who are willing to make a one-way trip to Mars, turning the Red Planet, Venus, or elsewhere into a “new frontier” where people can buy up land will first require some serious advances in technology, some serious terraforming, or both.
As it stands, the environments of Mars, Venus, the Moon, and the outer Solar System are all hostile to life as we know it. Even with the requisite commitment of resources and people willing to be the “first wave”, life would be very difficult for those living out there. And this situation would not change for centuries or even millennia. Like it not, transforming a planet’s ecology is very slow, laborious work.
Artist’s concept of a Martian astronaut standing outside the Mars One habitat. Credit: Bryan Versteeg/Mars One
Conclusion:
So… after considering all of the places where humanity could colonize and terraform, what it would take to make that happen, and the difficulties in doing so, we are once again left with one important question. Why should we? Assuming that our very survival is not at stake, what possible incentives are there for humanity to become an interplanetary (or interstellar) species?
Perhaps there is no good reason. Much like sending astronauts to the Moon, taking to the skies, and climbing the highest mountain on Earth, colonizing other planets may be nothing more than something we feel we need to do. Why? Because we can! Such a reason has been good enough in the past, and it will likely be sufficient again in the not-too-distant future.
This should is no way deter us from considering the ethical implications, the sheer cost involved, or the cost-to-benefit ratio. But in time, we might find that we have no choice but to get out there, simply because Earth is just becoming too stuffy and crowded for us!
A new paper says that a Super-Earth may have formed in our Solar System and been swallowed by the Sun. Image Credit: ESA/Hubble, M. Kornmesser
55 Cancri-e was once touted as one of the most exotic exo-planets ever discovered. Mass and radius modelling led some astronomers to speculate that its interior could be rich in carbon. And that much carbon crushed together under extreme pressure = diamonds. That’s how it got its nickname “Diamond Planet.”
But 55 Cancri-e—now named “Janssen” (Thank you International Astronomical Union!)—is even more exotic with the recent discovery of an atmosphere. A February 7th research paper in the Astrophysical Journal, by a team of European astronomers, reports that Janssen has an atmosphere rich in hydrogen. This makes Janssen the first exo-planet, that we know of, to have an atmosphere.
The team used the Wide Field Camera 3 (WDF3) on the Hubble Space Telescope, and a new scanning technique, to gain an understanding of Janssen’s atmosphere. Along with hydrogen, the team also found helium, and potentially, hydrogen cyanide.
Given Janssen’s surface temperature of 2000 K (1727 C), and its proximity to its host star, the existence of an atmosphere is surprising. The team suspects that the hydrogen-rich atmosphere is left over from the planet’s formation 8 billion years ago, and is a remnant of the nebula that the planet and star formed from.
“Our observations of 55 Cancri e’s atmosphere suggest that the planet has managed to cling on to a significant amount of hydrogen and helium from the nebula from which it formed,” said Angelos Tsiaras, a PhD student at UCL, who helped develop the new scanning technique. “This is a very exciting result because it’s the first time that we have been able to find the spectral fingerprints that show the gases present in the atmosphere of a super-Earth.”
Super-Earths are the most common type of planet in our galaxy, though none exist in our solar system. They are called super-Earths because they have more mass than Earth, but are smaller than the gas giants. A greater understanding of super-Earths should mean a greater understanding of the most common type of planet around.
“This result gives a first insight into the atmosphere of a super-Earth. We now have clues as to what the planet is currently like, how it might have formed and evolved, and this has important implications for 55 Cancri e and other super-Earths,” said Professor Giovanna Tinetti of UCL.
The existence of hydrogen cyanide in Janssen’s atmosphere is also significant. Its presence indicates a carbon-rich atmosphere. This supports the idea that Janssen is a diamond planet, though that conclusion is still far from certain. “If the presence of hydrogen cyanide and other molecules is confirmed in a few years time by the next generation of infrared telescopes, it would support the theory that this planet is indeed carbon rich and a very exotic place,” said Professor Jonathan Tennyson, UCL.
The team has used their new technique on 2 other super-Earths, but no atmosphere was found.
55-Cancri e is about 40 light years from Earth. Its host star is slightly smaller, cooler, and a little dimmer than our Sun, and its year is shorter than an Earth day.
