This artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. Credit: NASA Ames/JPL-Caltech/T. Pyle
Scientists say NASA’s Kepler Space Telescope has discovered Earth’s “older, bigger first cousin” – a planet that’s about 60 percent bigger than our own, circling a sunlike star in an orbit that could sustain liquid water and perhaps life.
“Today, Earth is a little bit less lonely, because there’s a new kid on the block,” Kepler data analysis lead Jon Jenkins, a computer scientist at NASA’s Ames Research Center, said Thursday during a NASA teleconference about the find.
The alien world, known as Kepler-452b, is about 1,400 light-years away in the constellation Cygnus – too far away to reach unless somebody perfects interstellar transporters. But its discovery raises the bar yet again in the search for Earth 2.0, which is a big part of Kepler’s mission.
Jenkins said that Kepler-452b has a better than even chance of being a rocky planet (though there’s some question about that). Its size implies that it’s about five times as massive as Earth. He said the planet might be cloudier than Earth and volcanically active, based on geological modeling. Visiting Earthlings would weigh twice as much as they did on Earth – until they walked around for a few weeks and “lost some serious pounds,” he joked.
An artist’s impression shows the surface of Kepler 452b. In the scenario depicted here, the planet is just entering a runaway greenhouse phase of its climate history. Kepler 452b could be giving us a preview of what Earth will undergo more than a billion years from now as the sun ages and grows brighter. Credit: Danielle Futselaar / SETI Institute
The planet is about 5 percent farther from its parent star than Earth is from our sun, with a year that lasts 385 days. Its sun is 10 percent bigger and 20 percent brighter than our sun, with the same classification as a G2 dwarf. But Kepler-452b’s star is older than our 4.6 billion-year-old home star – which suggests the cosmic conditions for life could be long-lasting.
“It’s simply awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star, which is longer than the age of the Earth,” Jenkins said. Models for planetary development suggest that Kepler-452b would experience an increasing warming trend and perhaps a runaway greenhouse effect as it aged, he said.
Kepler-452b’s advantages trump the mission’s earlier planetary discoveries. One involved a rocky planet, just a little bigger than Earth, that was found in its parent star’s habitable zone – that is, the kind of orbit where liquid water could exist. But that star, known as Kepler-186, is a shrunken red dwarf rather than a close analog to the sun.
Kepler research scientist Jeff Coughlin said it’s not clear how hospitable a planet circling a red dwarf might be. A rocky planet in the right orbit around a sunlike star is a surer bet. “We’re here on Earth, we know there’s life here,” he said.
Scientists said Kepler-452b is on the target list for the SETI Institute’s search for radio signals from extraterrestrial civilizations, using the Allen Telescope Array in California – but no alien detection has been reported. “So far, the 452b-ians have been coy,” Seth Shostak, the institute’s senior astronomer and director of the Center for SETI Research, told Universe Today in an email.
This size and scale of the Kepler-452 system compared alongside our own solar system, plus another planetary system with a habitable-zone planet known as Kepler-186f. The Kepler-186 system has a faint red dwarf star.
John Grunsfeld, NASA’s associate administrator for science, characterized the newly announced planet as the “closest twin” to Earth discovered so far. However, he said further analysis of the Kepler data may turn up even closer relatives.
Launched in 2009, Kepler detects alien worlds by looking for the faint dimming of a star as a planet crosses its disk. The SUV-sized telescope has spotted more than 4,600 planet candidates.
So far, about 1,000 of those have been confirmed as planets using other methods, ranging from detecting their parent stars’ Doppler shifts to carefully measuring the time intervals between the passages of planets. For Kepler-452b, scientists used ground-based observations and computer models to estimate the mass and confirm the detection to a level of 99.76 percent, Jenkins said.
The findings were due to be published online Thursday by the Astrophysical Journal, Jenkins said. In addition to Kepler-452b, another 521 planet candidates have been added to the mission’s checklist – including 12 candidates that appear to be one to two times as wide as Earth and orbit in their parent stars’ habitable zones. Nine of the stars are similar to our own sun in size and temperature, NASA said in a news release.
There’s sure to be more to come. In 2013, Kepler was crippled by failures of its fine-pointing navigation system, but it returned to its planet-hunting mission last year, thanks to some clever tweaking that makes use of the solar wind as an extra stabilizer. “It’s kind of the best-worst thing that ever happened to Kepler,” Jenkins said.
With astronomers discovering new planets and other celestial objects all the time, you may be wondering what the newest planet to be discovered is. Well, that depends on your frame of reference. If we are talking about our Solar System, then the answer used to be Pluto, which was discovered by the American astronomer Clyde William Tombaugh in 1930.
Unfortunately, Pluto lost its status as a planet in 2006 when it was reclassified as a dwarf planet. Since then, another contender has emerged for the title of “newest planet in the Solar System” – a celestial body that goes by the name of Eris – while beyond our Solar System, thousands of new planets are being discovered.
But then, the newest planet might be the most recently discovered extrasolar planet. And these are being discovered all the time.
Illustration of the orbit of Kepler-432b (inner, red) in comparison to the orbit of Mercury around the Sun (outer, orange). Credit: Dr. Sabine Reffert.
Astronomers are calling Kepler-432b a ‘maverick’ planet because everything about this newly found exoplanet is an extreme, and is unlike anything we’ve found before. This is a giant, dense planet orbiting a red giant star, and the planet has enormous temperature swings throughout its year. In addition to all these extremes, there’s another reason you wouldn’t want to live on Kepler 432b: its days are numbered.
“In less than 200 million years, Kepler-432b will be swallowed by its continually expanding host star,” said Mauricio Ortiz, a PhD student at Heidelberg University who led one of the two studies of the planet. “This might be the reason why we do not find other planets like Kepler-432b – astronomically speaking, their lives are extremely short.”
Kepler-432b is one of the densest and massive planets ever found. The planet has six times the mass of Jupiter, but is about the same size. The shape and the size of its orbit are also unusual, as the orbit is very small (52 Earth days) and highly elongated. The elliptical orbit brings Kepler-432b both incredibly close and very far away from its host star.
“During the winter season, the temperature on Kepler-432b is roughly 500 degrees Celsius,” said Dr. Sabine Reffert from the Königstuhl observatory, which is part of the Centre for Astronomy. “In the short summer season, it can increase to nearly 1,000 degrees Celsius.”
Dr. Davide Gandolfi, also from the Königstuhl observatory, said that the star Kepler-432b is orbiting has already exhausted the nuclear fuel in its core and is gradually expanding. Its radius is already four times that of our Sun and it will get even larger in the future.
While Kepler-432b was previously identified as a transiting planet candidate by the NASA Kepler satellite mission, two research groups of Heidelberg astronomers independently made further observations of this rare planet, acquiring the high-precision measurements needed to determine the planet’s mass. Both groups of researchers used the 2.2-metre telescope at Calar Alto Observatory in Andalucía, Spain to collect data. The group from the state observatory also observed Kepler-432b with the Nordic Optical Telescope on La Palma (Canary Islands).
An animated history of planetary detection, from 1750 to 2015. It shows the period (x-axis), mass (y-axis), radius (circle size) and detection method (color) of the 1800 plus planets now known. Credit and copyright: Hugh Osborn.
Early astronomers realized some of the “stars” in the sky were planets in our Solar System, and really, only then did we realize Earth is a planet too. Now, we’re finding planets around other stars, and thanks to the Kepler Space Telescope, we’re able to find planets that are even smaller than Earth.
This great new graphic of the history of planetary detection was put together by Hugh Osborn, a PhD student at the University of Warwick, who works with data from the WASP (Wide Angle Search for Planets) and NGTS (Next Generation Transit Survey) telescope surveys to discover exoplanets. It starts with the first real “discovery’ of a planet — Uranus in 1781 by William and Caroline Herschel.
“The idea of this plot is to compare our own Solar System (with planets plotted in dark blue) against the newly-discovered extrasolar worlds,” wrote Osborn on his website. “Think of this plot as a projection of all 1873 worlds onto our own solar system, with the Sun (and all other stars) at the far left. As you move out to the right, the orbital period of the planets increases, and correspondingly (thanks to Kepler’s Third Law), so does the distance from the star. Moving upwards means the mass of the worlds increase, from Moon-sized at the base to 10,000 times that of Earth at the top (30 Jupiter Masses).”
You’ll notice a few “clusters” as time moves along. The circles in dark blue are the planets in our Solar System; light blue are planets found by radial velocity. Then in maroon are planets found by direct imaging, followed by orange for microlensing and green for transits.
The first batch of exoplanets were the massive ‘Hot Jupiters’, which were the first exoplanets found “simply because they are easiest to find,” using the radial velocity method. Then you’ll see clusters found by the other methods ending with the big batch found by Kepler.
“This clustering shows that there are more Earth and super-Earth sized planets than any other,” said Osborn. “Hopefully we can begin to probe below it’s limit and into the Earth-like regime, where thousands more worlds should await!”
On reddit, Osborn also provided great, short explanations of the various methods used to detect planets, which we’ll include below:
Radial Velocity
Planets orbit thanks to gravitational attraction from their star’s mass. But the mass of the planet also has an effect on the star – pulling it around in a tiny circle once every orbit. Astronomers can split the light from a star up into it’s colours, which have an atomic barcode of absorption lines in. These lines shift position as the star moves – the light is effectively compressed to bluer colours when moving towards and pulled to redder colours when moving away.
So, by measuring this to-and-fro (radial) velocity, and finding periodic signals, astronomers can detect the tug of distant exoplanets.
Direct Imaging
This is easier to get your head around – point a big telescope at a star and directly image a planet around it. This only work for the biggest young planets as these are warmest, so glow brightest in the infra-red (like a red-hot piece of Iron). To find the planet in the glare of it’s star, the starlight needs to be suppressed. This is done by either blocking it out with a starshade, or digitally combining the images in such a way to remove the central star, revealing new exoplanets.
Microlensing
Einstein’s general theory of relativity shows that mass bends space time. This means that light can be bent by massive objects, and even act like a lens. Occasionally a star with a planetary system passes in front of a distant star. The light from the distant star is bent and lensed by both the star and the planet, giving two sharp increases in brightness over a few days – one for the star and one for the planet. The amount of lensing gives the mass of the planets, and the time between the events gives us the distance from their star. More info
Transits
When a planet crosses in front of it’s star, it blocks out a small portion of sunlight depending on it’s size. We only see the star as a single point, but we can infer the presence of a planet from the dip in light. When this repeats, we get a period. This is how we have found more than 1000 of the current crop of ~1800 exoplanets!
Thanks to Hugh Osborn for sharing his expertise with Universe Today!
An artist rendition of Kepler-444 planetary system, which hosts five planets, all smaller than Earth. Credit: Tiago Campante, University of Birmingham, UK.
Using data from the Kepler space telescope, an international group of astronomers has discovered the oldest known planetary system in the galaxy – an 11 billion-year-old system of five rocky planets that are all smaller than Earth. The team says this discovery suggests that Earth-size planets have formed throughout most of the Universe’s 13.8-billion-year history, increasing the possibility for the existence of ancient life – and potentially advanced intelligent life — in our galaxy.
“The fact that rocky planets were already forming in the galaxy 11 billion years ago suggests that habitable Earth-like planets have probably been around for a very long time, much longer than the age of our Solar System,” said Dr. Travis Metcalfe, Senior Research Scientist Space Science Institute, who was part of the team that used the unique method of asteroseismology to determine the age of the star.
The star, named Kepler-444, is about 25 percent smaller than our Sun and is 117 light-years from Earth. The system of five known planets is very compact, and all five planets orbit the parent star in less than 10 days, or within 0:08 AU, roughly one-fifth the size of Mercury’s orbit.
“The star is slightly cooler than the Sun (around 5000 K at the surface, compared to 5800 K),” Metcalfe told Universe Today, “but the planets in this system are still expected to be highly irradiated and inhospitable to life,” with little to no atmospheres.
The team wrote in their paper that the system’s habitable zone lies 0:47 AU from the parent star and so all planets orbit well interior to the inner edge of Kepler-444’s ‘Goldilocks zone.’
The team was led by Tiago Campante, a research fellow at the University of Birmingham in the UK.
The planets were found by analyzing four years of Kepler data, as the spacecraft had nearly continuous observations of Kepler-444 during Kepler’s active mission. The space telescope took high-precision measurements of changes in brightness in stars in its field of view. There are tiny changes in brightness when planets pass in front of their stars.
Transit signals indicated five planets orbiting Kepler-444, although this star has a binary companion, an M-dwarf, and it was a tedious process to tease out all the data to determine what were planets and not other stars, as well as which star the planets were orbiting. An image of the Kepler-444 star system using the NIRC2 near-infrared imager on the Keck II telescope. Credit: Tiago Campante et al.
Metcalfe said the the job of “validating” the planets by ruling out all of the other possible “false positive” scenarios is always a big challenge for Kepler targets.
But asteroseismology was used to directly measure the precise age of the star. Asteroseismology, or stellar seismology is basically listening to a star by measuring sound waves. The sound waves travel into the star and bring information back up to the surface. The waves cause oscillations that Kepler observes as a rapid flickering of the star’s brightness.
How can this help determine a star’s age?
“As a star ages, it converts hydrogen into helium in the core,” Metcalfe said via email. “This changes the mean density of the star over time, and asteroseismology provides a very precise measure of the mean density (from the regular spacing of the individual oscillation frequencies).”
Metcalfe said that in this case, the uncertainty on the age of the star (and thus the planets, which formed essentially at the same time) is only 9%, compared to a typical uncertainty of 30-50% from other methods based on rotation (gyrochronology) or other properties of the star.
The team also noted in their paper that this finding may also help to pinpoint the beginning of the era of planet formation.
“I think this system has a lot to teach us about planet formation and the long-term evolution of planetary systems,” said Darin Ragozzine, a professor at Florida Institute of Technology and a a member of the discovery team, who specializes in multi-transiting systems. “With an age of 11.2 billion years, it means that this system formed near the beginning of the age of the Universe.”
The team wrote that this finding implies that small, Earth-size, planets may have readily formed at early epochs in the Universe’s history, even when metals were more scarce.
“By the time Earth formed, this star and its planetary system were already older than our planet is today,” Ragozzine told Universe Today. “We don’t know for sure if this system has stayed the same the whole time, but it is amazing to think that the little inner planet has gone around the star about a trillion times!”
To find out more about asteroseismology, check out a website called the Pale Blue Dot Project. Metcalfe launched a non-profit organization to help raise research funds for the Kepler Asteroseismic Science Consortium. The Pale Blue Dot Project allows people to adopt a star to support asteroseismology, since there is no NASA funding for asteroseismology.
“Much of the expertise for this exists in Europe and not in the US, so as a cost saving measure NASA outsourced this particular research for the Kepler mission,” said Metcalfe, “and NASA can’t fund researchers in other countries.”
Metcalfe added that the “adopt a star” program supported the asteroseismic analysis of Kepler-444, “determining the precise age that makes this ancient planetary system so interesting… This private funding from citizens around the world has been an invaluable resource to facilitate our research and fuel amazing discoveries like this one.”
Astronomers watching the repeated and drawn-out dimming of a relatively nearby Sun-like star have interpreted their observations to indicate an eclipse by a gigantic exoplanet’s complex ring system, similar to Saturn’s except much, much bigger. What’s more, apparent gaps and varying densities of the rings imply the presence of at least one large exomoon, and perhaps even more in the process of formation!
J1407 is a main-sequence orange dwarf star about 434 light-years away*. Over the course of 57 days in spring of 2007 J1407 underwent a “complex series of deep eclipses,” which an international team of astronomers asserts is the result of a ring system around the massive orbiting exoplanet J1407b.
“This planet is much larger than Jupiter or Saturn, and its ring system is roughly 200 times larger than Saturn’s rings are today,” said Eric Mamajek, professor of physics and astronomy at the University of Rochester in New York. “You could think of it as kind of a super Saturn.”
The observations were made through the SuperWASP program, which uses ground-based telescopes to watch for the faint dimming of stars due to transiting exoplanets.
The first study of the eclipses and the likely presence of the ring system was published in 2012, led by Mamajek. Further analysis by the team estimates the number of main ring structures to be 37, with a large and clearly-defined gap located at about 0.4 AU (61 million km/37.9 million miles) out from the “super Saturn” that may harbor a satellite nearly as large as Earth, with an orbital period of two years.
Watch an animation of the team’s analysis of the J1407/J1407b eclipse below:
The entire expanse of J1407b’s surprisingly dense rings stretches for 180 million km (112 million miles), and could contain an Earth’s worth of mass.
“If we could replace Saturn’s rings with the rings around J1407b,” said Matthew Kenworthy from Leiden Observatory in the Netherlands and lead author of the new study, “they would be easily visible at night and be many times larger than the full Moon.”
Saturn’s relatively thin main rings are about 250,000 km (156,000 miles) in diameter. (Image: NASA/JPL-Caltech/SSI/J. Major)
These observations could be akin to a look back in time to see what Saturn and Jupiter were like as their own system of moons were first forming.
“The planetary science community has theorized for decades that planets like Jupiter and Saturn would have had, at an early stage, disks around them that then led to the formation of satellites,” according to Mamajek. “However, until we discovered this object in 2012, no one had seen such a ring system. This is the first snapshot of satellite formation on million-kilometer scales around a substellar object.”
J1407b itself is estimated to contain 10-40 times the mass of Jupiter – technically, it might even be a brown dwarf.
Further observations will be required to observe another transit of J1407b and obtain more data on its rings and other physical characteristics as its orbit is about ten Earth-years long. (Luckily 2017 isn’t that far off!)
The team’s report has been accepted for publication in the Astrophysical Journal.
Note: the originally published version of this article described J1407 at 116 light-years away. It’s actually 133 parsecs, which equates to about 434 light-years. Edited above. – JM
A NASA "travel poster" touting the benefits of exoplanet Kepler-16b, which has two Suns. Credit: NASA/JPL-Caltech
What beauty, and what awesome travel slogans! NASA’s Jet Propulsion Laboratory has created a set of “Exoplanet Travel Posters” to bring you — at least in your imagination — to actual exoplanets.
Whether you have a fancy for skydiving, or doing astronomy with two Suns, it appears there is a spot to whet your imagination. We have another example of the fantastic artwork below.
You can download all three posters so far in glorious high-definition here. These are NASA’s descriptions for each of the worlds described so far:
Kepler-186f is the first Earth-size planet discovered in the potentially ‘habitable zone’ around another star, where liquid water could exist on the planet’s surface. Its star is much cooler and redder than our Sun. If plant life does exist on a planet like Kepler-186f, its photosynthesis could have been influenced by the star’s red-wavelength photons, making for a color palette that’s very different than the greens on Earth.
Twice as big in volume as the Earth, HD 40307g straddles the line between “Super-Earth” and “mini-Neptune” and scientists aren’t sure if it has a rocky surface or one that’s buried beneath thick layers of gas and ice. One thing is certain though: at eight time the Earth’s mass, its gravitational pull is much, much stronger.
A NASA “travel poster” showing off how fun skydiving would be on HD 40307g, a planet that is somewhere in size between a “super-Earth” or “mini-Neptune.” Credit: NASA/JPL-Caltech
Like Luke Skywalker’s planet “Tatooine” in Star Wars, Kepler-16b orbits a pair of stars. Depicted here as a terrestrial planet, Kepler-16b might also be a gas giant like Saturn. Prospects for life on this unusual world aren’t good, as it has a temperature similar to that of dry ice. But the discovery indicates that the movie’s iconic double-sunset is anything but science fiction.
The posters are not only clever, but appear to be homages to the Work Projects Administration’s “See America” posters of the 1930s and 1940s, which you can browse through on the Library of Congress’ website.
Magnetic loops carry gas and dust above disks of planet-forming material circling stars, as shown in this artist's conception. These loops give off extra heat, which NASA's Spitzer Space Telescope detects as infrared light. The colors in this illustration show what an alien observer with eyes sensitive to both visible light and infrared wavelengths might see. Credit: NASA/JPL-Caltech/R. Hurt (IPAC)
With a big universe around us, where the heck do you point your telescope when looking for planets? Bigger observatories are set to head to orbit in the next decade, including NASA’s James Webb Space Telescope and the European Space Agency’s PLATO (PLAnetary Transits and Oscillations of stars). Telling them where to look will be a challenge.
But it’s less of an issue thanks to the dedicated efforts of amateurs. Volunteers sifting through data from a NASA mission called WISE (Wide-field Infrared Survey Explorer) have now classified an astounding one million potential debris disks and disks surrounding young stars.
“Combing through objects identified by WISE during its infrared survey of the entire sky, Disk Detective aims to find two types of developing planetary environments,” NASA stated in a press release touting the achievement.
“The first, known as a YSO disk, typically is less than 5 million years old, contains large quantities of gas, and often is found in or near young star clusters. The second planetary habitat, known as a debris disk, tends to be older than 5 million years, holds little or no gas, and possesses belts of rocky or icy debris that resemble the asteroid and Kuiper belts found in our own solar system.”
What’s more astounding is how little time it took — the program Disk Detective was only launched in January 2014. These are ripe environments in which young planets can form, providing plenty of spots for telescopes to turn their eyes. The search is expected to go on through 2018.
An artist's conception of one of the newly released exo-worlds, a planet orbiting an ancient planetary nebula. Credit: David A. Aguilar/CfA.
A fascinating set of finds was announced today at the 225th meeting of the American Astronomical Society (AAS), currently underway this week in Seattle, Washington. A team of astronomers announced the discovery of eight new planets potentially orbiting their host stars in their respective habitable zones. Also dubbed the ‘Goldilocks Zone,’ this is the distance where — like the tempting fairytale porridge — it’s not too hot, and not too cold, but juuusst right for liquid water to exist.
And chasing the water is the name of the game when it comes to hunting for life on other worlds. Two of the discoveries announced, Kepler-438b and Kepler-442b, are especially intriguing, as they are the most comparable to the Earth size-wise of any exoplanets yet discovered.
“Most of these planets have a good chance of being rocky, like Earth,” said Guillermo Torres in a recent press release. Guillermo is the lead author in the study for the Harvard-Smithsonian Center for Astrophysics (CfA).
This also doubles the count of suspected terrestrial exo-worlds — planets with less than twice the diameter of the Earth — inferred to orbit in the habitable zone of their host stars.
Fans on exoplanet science will remember the announcement of the first prospective Earth-like world orbiting in the habitable zone of its host star, Kepler-186f announced just last year.
The Kepler Space Telescope looks for planets used a technique known as the transit method. If a planet is orbiting its host star along our line of sight, a small but measurable dip in the star’s brightness occurs. This has advantages over the radial velocity technique because it allows researchers to pin down the hidden planet’s orbit and size much more precisely. The transit method is biased, however, to planets close in to its host which happen to lie along our solar system-bound line of sight. Kepler may miss most exo-worlds inclined out of its view, but it overcomes this by staring at thousands of stars.
The launch of Kepler from the Cape in 2009. Credit: NASA/Kim Shiflett.
Launched in 2009, Kepler has wrapped up its primary phase of starring at a patch of sky along the plane of the Milky Way in the directions of the constellations of Cygnus, Lyra and Hercules, and is now in its extended K2 mission using the solar wind pressure as a 3rd ‘reaction wheel’ to carry out targeted searches along the ecliptic plane.
Both newly discovered worlds highlighted in today’s announcement orbit distant red dwarf stars. Kepler-438 b is estimated to be 12% larger in diameter than the Earth, and Kepler-442 b is estimated by the team to be 33% larger. These worlds have a 70% and 60% chance of being rocky, respectively. For comparison, Ice giant planet Uranus is 4 times the diameter of the Earth, and over 14 times more massive.
A comparison of the new exoplanet finds between Earth and Jupiter. Credit: NASA/Kepler.
“We don’t know for sure whether any of the planets in our sample are truly habitable,” Said CfA co-researcher in the study David Kipping. All we can say is that they’re promising candidates.”
The idea of habitable worlds around red dwarf stars is a tantalizing one. These stars are fainter and cooler than our Sun, and 7.5% to 50% as massive. They also have two primary factors going for them: they’re the most common type of stars in the universe, and they have life spans measured in trillions of years, much longer than the current age of the universe. If life could go from muck to making microwave dinners here on Earth in just a few billion years, it’s had lots longer to do the same on worlds orbiting red dwarf stars.
There is, however, one catch: the habitable zone surrounding a red dwarf is much closer in to its host star, and any would-be planet is subject to frequent surface-sterilizing flares. Perhaps a world with a synchronous rotation might be spared this fate and feature a habitable hemisphere well inside the snow line permanently turned away from its host.
The team made these discoveries by sifting though Kepler’s preliminary finds that are termed KOI’s, or Kepler Objects of Interest. Though these potential discoveries were far too small to pin down their masses using the traditional method, the team employed a program named BLENDER to statically validate the finds. BLENDER has been employed before in concert with backup observations for extremely tiny exoplanet discoveries. Torres and Francois Fressin developed the BLENDER program, and it is currently run on the massive Pleiades supercomputer at NASA Ames.
It was also noted in today’s press conference that two KOIs awaiting validation — 5737.01 and 2194.03 — may also prove to be terrestrial worlds orbiting Sun-like stars that are possibly similar in size to the Earth.
The proposed target regions for the Kepler K2 mission. Credit: NASA/Kepler.
But don’t plan on building an interstellar ark and heading off to these newly found worlds just yet. Kepler-438b sits 470 light years from Earth, and Kepler-442b is even farther away at 1,100 light years. And we’ll also add our usual caveat and caution that, from a distance, the planet Venus in our own solar system might look like a tempting vacation spot. (Spoiler alert: it’s not).
Still, these discoveries are fascinating finds and add to the growing menagerie of exoplanet systems. These will also serve as great follow up targets for TESS, Gaia and LSST survey, all set to add to our exoplanet knowledge in the coming decade.
The LSST mirror in the Tuscon Mirror Lab. (Photo by author).
And to think, I remember growing up as a child of the 1970s reading that exoplanet detections were soooo difficult that they might never occur in our lifetime… now, fast-forward to 2015, and we’re beginning to classify and characterize other brave new solar systems in the modern Age of Exoplanet Science.
-Looking to observe red dwarf stars with your backyard scope? Check out our handy list.
The James Webb Space Telescope, scheduled for launch in 2018 may be the first to be capable of detecting biomarker gasses in the atmospheres of extrasolar planets. When an exoplanet passes between its star and Earth, an event called a transit, light that has passed through the planet’s atmosphere can be detected from a vantage point near Earth. When light passes through the exoplanet’s atmosphere, some wavelengths are absorbed and others transmitted. By analyzing the transmitted light spectrum, astronomers can learn the composition of the planet’s atmosphere. Astrobiologists hope to find biomarker gasses indicating the metabolic waste products of life. The oxygen in Earth’s atmosphere is a waste product of photosynthesis in plants and bacteria. The Webb telescope may be capable of conducting this test for planets larger than Earth (super-earths) transiting small stars. Space telescopes capable of conducting such research on a larger scale have been delayed by budget cuts.
Credit: NASA
In the movie “Avatar”, we could tell at a glance that the alien moon Pandora was teeming with alien life. Here on Earth though, the most abundant life is not the plants and animals that we are familiar with. The most abundant life is simple and microscopic. There are 50 million bacterial organisms in a single gram of soil, and the world wide bacterial biomass exceeds that of all plants and animals. Microbes can grow in extreme environments of temperature, salinity, acidity, radiation, and pressure. The most likely form in which we will encounter life elsewhere in our solar system is microbial.
Astrobiologists need strategies for inferring the presence of alien microbial life or its fossilized remains. They need strategies for inferring the presence of alien life on the distant planets of other stars, which are too far away to explore with spacecraft in the foreseeable future. To do these things, they long for a definition of life, that would make it possible to reliably distinguish life from non-life.
Unfortunately, as we saw in the first installment of this series, despite enormous growth in our knowledge of living things, philosophers and scientists have been unable to produce such a definition. Astrobiologists get by as best they can with definitions that are partial, and that have exceptions. Their search is geared to the features of life on Earth, the only life we currently know.
In the first installment, we saw how the composition of terrestrial life influences the search for extraterrestrial life. Astrobiologists search for environments that once contained or currently contain liquid water, and that contain complex molecules based on carbon. Many scientists, however, view the essential features of life as having to do with its capacities instead of its composition.
In 1994, a NASA committee adopted a definition of life as a “self-sustaining chemical system capable of Darwinian evolution”, based on a suggestion by Carl Sagan. This definition contains two features, metabolism and evolution, that are typically mentioned in definitions of life.
Metabolism is the set of chemical processes by which living things actively use energy to maintain themselves, grow, and develop. According to the second law of thermodynamics, a system that doesn’t interact with its external environment will become more disorganized and uniform with time. Living things build and maintain their improbable, highly organized state because they harness sources of energy in their external environment to power their metabolism.
Plants and some bacteria use the energy of sunlight to manufacture larger organic molecules out of simpler subunits. These molecules store chemical energy that can later be extracted by other chemical reactions to power their metabolism. Animals and some bacteria consume plants or other animals as food. They break down complex organic molecules in their food into simpler ones, to extract their stored chemical energy. Some bacteria can use the energy contained in chemicals derived from non-living sources in the process of chemosynthesis.
In a 2014 article in Astrobiology, Lucas John Mix, a Harvard evolutionary biologist, referred to the metabolic definition of life as Haldane Life after the pioneering physiologist J. B. S. Haldane. The Haldane life definition has its problems. Tornadoes and vorticies like Jupiter’s Great Red Spot use environmental energy to sustain their orderly structure, but aren’t alive. Fire uses energy from its environment to sustain itself and grow, but isn’t alive either.
Despite its shortcomings, astrobiologists have used Haldane definition to devise experiments. The Viking Mars landers made the only attempt so far to directly test for extraterrestrial life, by detecting the supposed metabolic activities of Martian microbes. They assumed that Martian metabolism is chemically similar to its terrestrial counterpart.
One experiment sought to detect the metabolic breakdown of nutrients into simpler molecules to extract their energy. A second aimed to detect oxygen as a waste product of photosynthesis. A third tried to show the manufacture of complex organic molecules out of simpler subunits, which also occurs during photosynthesis. All three experiments seemed to give positive results, but many researchers believe that the detailed findings can be explained without biology, by chemical oxidizing agents in the soil.
In 1976, two Viking spacecraft landed on Mars. The image is of a model of the Viking lander, along with astronomer and pioneering astrobiologist Carl Sagan. Each lander was equipped with life detection experiments designed to detect life based on its metabolic activities. These activities were assumed to be chemically similar to those of Earthly organisms. The three experiments included: 1) The labeled release experiment, in which radioactively labeled organic nutrients were added to Martian soil. If organisms were present, it was assumed that their metabolism would involve breaking down the nutrients for their energy content and releasing labeled carbon dioxide as a waste product. 2) The gas exchange experiment, in which Martian soil was provided with nutrients and light and monitored for the release of oxygen. On Earth, organisms that capture the energy of sunlight through the process of photosynthesis, like plants and some bacteria, release oxygen as a waste product. 3) The pyrolytic release experiment, in which Martian soil was placed in a chamber with radioactively labeled carbon dioxide. If there were organisms in the soil that photosynthesized like those on Earth, their metabolic processes would take up the gas and use the energy of sunlight to manufacture more complex organic molecules. Radioactive carbon would be given off when those more complex molecules were broken down by heating the sample. All three experiments produced what seemed like positive results. However, most scientists rejected this interpretation because the details of many of the results could be explained by supposing that there were chemical oxidizing agents in the soil instead of life, and because Viking failed to detect organic materials in Martian soil. This interpretation, especially for the labeled release experiment, remains controversial to this day and may need to be revisited based on recent findings. Credits: NASA/Jet Propulsion Laboratory, Caltech
Some of the Viking results remain controversial to this day. At the time, many researchers felt that the failure to find organic materials in Martian soil ruled out a biological interpretation of the metabolic results. The more recent finding that Martian soil actually does contain organic molecules that might have been destroyed by perchlorates during the Viking analysis, and that liquid water was once abundant on the surface of Mars lend new plausibility to the claim that Viking may have actually succeeded in detecting life. By themselves, though, the Viking results didn’t prove that life exists on Mars nor rule it out.
Most of the methane in Earth’s atmosphere is released by living organisms or their remains. Subterranean bacterial ecosystems that use chemosynthesis as a source of energy are common, and they produce methane as a metabolic waste product. Unfortunately, there are also non-biological geochemical processes that can produce methane. So, once more, Martian methane is frustratingly ambiguous as a sign of life.
Extrasolar planets orbiting other stars are far too distant to visit with spacecraft in the foreseeable future. Astrobiologists still hope to use the Haldane definition to search for life on them. With near future space telescopes, astronomers hope to learn the composition of the atmospheres of these planets by analyzing the spectrum of light wavelengths reflected or transmitted by their atmospheres. The James Webb Space Telescope scheduled for launch in 2018, will be the first to be useful in this project. Astrobiologists want to search for atmospheric biomarkers; gases that are metabolic waste products of living organisms.
Once more, this quest is guided by the only example of a life-bearing planet we currently have; Earth. About 21% of our home planet’s atmosphere is oxygen. This is surprising because oxygen is a highly reactive gas that tends to enter into chemical combinations with other substances. Free oxygen should quickly vanish from our air. It remains present because the loss is constantly being replaced by plants and bacteria that release it as a metabolic waste product of photosynthesis.
Traces of methane are present in Earth’s atmosphere because of chemosynthetic bacteria. Since methane and oxygen react with one another, neither would stay around for long unless living organisms were constantly replenishing the supply. Earth’s atmosphere also contains traces of other gases that are metabolic byproducts.
In general, living things use energy to maintain Earth’s atmosphere in a state far from the thermodynamic equilibrium it would reach without life. Astrobiologists would suspect any planet with an atmosphere in a similar state of harboring life. But, as for the other cases, it would be hard to completely rule out non-biological possibilities.
Besides metabolism, the NASA committee identified evolution as a fundamental ability of living things. For an evolutionary process to occur there must be a group of systems, where each one is capable of reliably reproducing itself. Despite the general reliability of reproduction, there must also be occasional random copying errors in the reproductive process so that the systems come to have differing traits. Finally, the systems must differ in their ability to survive and reproduce based on the benefits or liabilities of their distinctive traits in their environment. When this process is repeated over and over again down the generations, the traits of the systems will become better adapted to their environment. Very complex traits can sometimes evolve in a step-by-step fashion.
Mix named this the Darwin life definition, after the nineteenth century naturalist Charles Darwin, who formulated the theory of evolution. Like the Haldane definition, the Darwin life definition has important shortcomings. It has trouble including everything that we might think of as alive. Mules, for example, can’t reproduce, and so, by this definition, don’t count as being alive.
Despite such shortcomings, the Darwin life definition is critically important, both for scientists studying the origin of life and astrobiologists. The modern version of Darwin’s theory can explain how diverse and complex forms of life can evolve from some initial simple form. A theory of the origin of life is needed to explain how the initial simple form acquired the capacity to evolve in the first place.
The chemical systems or life forms found on other planets or moons in our solar system might be so simple that they are close to the boundary between life and non-life that the Darwin definition establishes. The definition might turn out to be vital to astrobiologists trying to decide whether a chemical system they have found really qualifies as a life form. Biologists still don’t know how life originated. If astrobiologists can find systems near the Darwin boundary, their findings may be pivotally important to understanding the origin of life.
Can astrobiologists use the Darwin definition to find and study extraterrestrial life? It’s unlikely that a visiting spacecraft could detect to process of evolution itself. But, it might be capable of detecting the molecular structures that living organisms need in order to take part in an evolutionary process. Philosopher Mark Bedau has proposed that a minimal system capable of undergoing evolution would need to have three things: 1) a chemical metabolic process, 2) a container, like a cell membrane, to establish the boundaries of the system, and 3) a chemical “program” capable of directing the metabolic activities.
Here on Earth, the chemical program is based on the genetic molecule DNA. Many origin-of-life theorists think that the genetic molecule of the earliest terrestrial life forms may have been the simpler molecule ribonucleic acid (RNA). The genetic program is important to an evolutionary process because it makes the reproductive copying process stable, with only occasional errors.
Both DNA and RNA are biopolymers; long chainlike molecules with many repeating subunits. The specific sequence of nucleotide base subunits in these molecules encodes the genetic information they carry. So that the molecule can encode all possible sequences of genetic information it must be possible for the subunits to occur in any order.
Steven Benner, a computational genomics researcher, believes that we may be able to develop spacecraft experiments to detect alien genetic biopolymers. He notes that DNA and RNA are very unusual biopolymers because changing the sequence in which their subunits occur doesn’t change their chemical properties. It is this unusual property that allows these molecules to be stable carriers of any possible genetic code sequence.
DNA and RNA are both polyelectrolytes; molecules with regularly repeating areas of negative electrical charge. Benner believes that this is what accounts for their remarkable stability. He thinks that any alien genetic biopolymer would also need to be a polyelectrolyte, and that chemical tests could be devised by which a spacecraft might detect such polyelectrolyte molecules. Finding the alien counterpart of DNA is a very exciting prospect, and another piece to the puzzle of identifying alien life.
Deoxyribonucleic acid (DNA) is the genetic material for all known life on Earth. DNA is a biopolymer consisting of a string of subunits. The subunits consist of nucleotide base pairs containing a purine (adenine A, or guanine G) and a pyrimidine (thymine T, or cytosine C). DNA can contain nucleotide base pairs in any order without its chemical properties changing. This property is rare in biopolymers, and makes it possible for DNA to encode genetic information in the sequence of its base pairs. This stability is due to the fact that each base pair contains phosphate groups (consisting of phosphorus and oxygen atoms) on the outside with a net negative charge. These repeated negative charges make DNA a polyelectrolyte. Computational genomics researcher Steven Benner has hypothesized that alien genetic material will also be a polyelectrolyte biopolymer, and that chemical tests could therefore be devised to detect alien genetic molecules. Credit: Zephyris
In 1996 President Clinton, made a dramatic announcement of the possible discovery of life on Mars. Clinton’s speech was motivated by the findings of David McKay’s team with the Alan Hills meteorite. In fact, the McKay findings turned out to be just one piece to the larger puzzle of possible Martian life. Unless an alien someday ambles past our waiting cameras, the question of whether or not extraterrestrial life exists is unlikely to be settled by a single experiment or a sudden dramatic breakthrough. Philosophers and scientists don’t have a single, sure-fire definition of life. Astrobiologists consequently don’t have a single sure-fire test that will settle the issue. If simple forms of life do exist on Mars, or elsewhere in the solar system, it now seems likely that that fact will emerge gradually, based on many converging lines of evidence. We won’t really know what we’re looking for until we find it.
S. Tirard, M. Morange, and A. Lazcano, (2010), The definition of life: A brief history of an elusive scientific endeavor, Astrobiology, 10(10):1003-1009.
