A view of Mercury from MESSENGER’s October 2008 flyby (NASA / JHUAPL / Gordan Ugarkovic)
Every now and then a new gem of a color-composite appears in the Flickr photostream of Gordan Ugarkovic, and this one is the latest to materialize.
This is a view of Mercury as seen by NASA’s MESSENGER spacecraft during a flyby in October 2008. The image is a composite of twenty separate frames acquired with MESSENGER’s narrow-angle camera from distances ranging from 18,900 to 17,700 kilometers and colorized with color data from the spacecraft’s wide-angle camera. (North is to the right.)
Click the image for a closer look, and for an even bigger planet-sized version click here. Beautiful!
The images that made up this mosaic were taken two and a half years before MESSENGER entered orbit around Mercury on March 19, 2011 UT, becoming the first spacecraft ever to do so and making Mercury the final “classical” planet to be orbited by a manmade spacecraft.
Since that time MESSENGER has completed well over 1,000 orbits and taken more than 100,000 images of the first planet in the Solar System, which filled in most of our gaps in Mercury’s map and showed us many never-before-seen features of the planet’s Sun-scoured surface. And just this past year MESSENGER’s extended mission helped confirm what could be called its most important discovery of all: water ice on Mercury’s north pole.
With all that’s been achieved by MESSENGER in 2011 and 2012, 2013 is looking to be an interesting year!
“We learned a great deal about Mercury over the past year,” said MESSENGER Principal Investigator Sean Solomon of Columbia University’s Lamont-Doherty Earth Observatory. “The team published three dozen scientific and technical papers and delivered more than 150 presentations at national and international meetings. New measurements continue to stream back from our spacecraft, and we can look forward with excitement to many additional discoveries in 2013.”
Artist’s impression of the surface of Makemake, a dwarf planet beyond Pluto (ESO/L. Calçada/Nick Risinger)
It turns out there’s no air up there: the distant dwarf planet Makemake is surprisingly lacking in an atmosphere, according to findings made by astronomers using telescopes at ESO’s La Silla and Paranal observatories.
An international team of astronomers used the mountaintop telescopes to observe Makemake as it passed in front of a faint background star in April 2011, a brief stellar occultation that lasted only about a minute. By watching how the starlight was blotted out by Makemake, measurements could be made of the dwarf planet’s size, mass and atmosphere — or, in this case, its lack thereof… a finding which surprised some scientists.
“As Makemake passed in front of the star and blocked it out, the star disappeared and reappeared very abruptly, rather than fading and brightening gradually. This means that the little dwarf planet has no significant atmosphere,” said team leader José Luis Ortiz of the Instituto de Astrofísica de Andalucía in Spain. “It was thought that Makemake had a good chance of having developed an atmosphere — that it has no sign of one at all shows just how much we have yet to learn about these mysterious bodies.”
First discovered in 2005, Makemake is an icy dwarf planet about 2/3 the diameter of Pluto — and 19 AU further from the Sun (but not nearly as far as the larger Eris, which is over 96 AU away.) It was thought that Makemake might have a tenuous, seasonal atmosphere similar to what has been found on Pluto, but it now appears that it does not… at least not in any large-scale, global form.
Due to its small size, sheer distance and apparent lack of moons, making scientific observations of Makemake has been a challenge for astronomers. The April 2011 occultation allowed measurements to be made — even if only for a minute — that weren’t possible before, including first-ever calculations of the dwarf planet’s density and albedo.
As it turns out, Makemake’s albedo is about 0.77 — comparable to that of dirty snow… a reflectivity higher than Pluto’s but lower than that of Eris. Its density is estimated to be 1.7 ± 0.3 g/cm³, indicating a composition of mostly ice with some rock.
“Our new observations have greatly improved our knowledge of one of the biggest [icy bodies], Makemake — we will be able to use this information as we explore the intriguing objects in this region of space further,” said Ortiz.
The team’s research was presented in a paper “Albedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation” to appear in the November 22, 2012 issue of the journal Nature.
Inset image: Makemake imaged by Hubble in 2006. (NASA/JPL-Caltech)
Although space missions Voyager and Galileo observed evidence of volcanic activity on Io, it was a faint blue plume at the edge of Io’s limb in a highly-enhanced image from Voyager that first offered evidence of the moon’s turbulent nature.
You fancy yourself an armchair astronomer? A group of California researchers have stepped it up a notch by monitoring the intense volcanic eruptions on Jupiter’s strangest moon Io from the comfort of their home.
Io, the innermost of the four largest moons around Jupiter, or the Galilean moons, is the most volcanically active object in the Solar System with more than 400 active volcanoes spitting out plumes of sulfur and sulfur dioxide. Scientists think a gravitational tug-of-war with Jupiter is one cause of Io’s intense vulcanism. Researchers point out that most of the processes are not well understood. While Io’s eruptions can’t be seen directly from Earth, a team led by Frank Marchis, a researcher at the Carl Sagan Center of the SETI Institute have come up with an unique combination of Earth-based telescope arrays and archival imagery from the Voyager and Galileo probes, according to a press release. The team announced their findings at the 2012 Division of Planetary Sciences meeting today in Reno, Nevada.
“Since our first observation of Io in 2001 using the W. M. Keck II 10-m telescope from the top of Mauna Kea in Hawaii and its AO (adaptive optics) system, our group became very excited about the technology,” says Marchis. “We also began using AO at the Very Large Telescope in Chile, and at the Gemini North telescope in Hawaii. The technology has improved over the years, and the image quality and usefulness of those complex instruments has made them part of the essential instrument suite for large telescopes.”
A faint blue plume on a grainy and highly enhanced image from Voyager 1 first hinted at Io’s dynamic nature. Voyager’s cameras showed a bizarre terrain of volcanic fields, dark spots and active plumes. Scientists nicknamed it the “Pizza Moon.” NASA’s Galileo probe observed more than 160 active volcanoes in various stages of eruption during its looping tour of the solar system’s largest planet.
But crystal clear pictures from Galileo ceased in 2003. Observing a Moon-sized object at the incredible distance to Jupiter from Earth is a challenge because of the blurring caused by Earth’s stirring atmosphere. Since 2001, all large 8- to 10-meter telescopes have been equipped with adaptive optics that correct for that blur. Since 2003, Marchis and his team have gathered about 40 cycles of observations of Io in the near-infrared showing details as small as 100 kilometers, or 60 miles, on the surface of the moon.
Observations of several bright & young eruptions detected at short wavelengths (~2.1 microns) on the top and longer wavelengths (~3.2 microns) on the bottom since 2004 using the W. M. Keck 10-meter telescope (May 2004, Aug 2007, Sep 2007, July 2009), the Gemini North 8-meter telescope (Aug 2007), and the ESO VLT-Yepun 8-meter telescope (Feb 2007), all with their adaptive optics systems. The thermal signature of the Tvashtar outburst can be seen near the north pole on images collected in 2007. A new eruption on Pillan Patera was seen in Aug 2007. A young and bright eruption was detected on Loki Patera in July 2009. This is the last bright eruption that was detected in our survey; since then, Io’s volcanic activity has been quiescent. Credit: F. Marchis
“Spacecraft have only been able to capture fleeting glimpses of Io’s volcanoes, Voyager for a few months, Galileo a few years, and New Horizons a few days. Ground-based observations, on the other hand, can continue to monitor Io’s volcanoes over long time-scales. The more telescopes looking at Io, the better time coverage we can obtain.” Said Julie Rathbun from Redlands University, a planetary scientist not directly involved in this study but who has conducted monitoring of Io with NASA’s IRTF 3-meter telescope for more than 15 years. “AO observations from 8-10m class telescopes are a dramatic improvement in spatial resolution over previous ground-based observations. Soon they will not only be our only way to monitor Io’s volcanoes, but the best way. We should be making these observations more often.”
Simulation of observations of Io using the W. M. Keck telescope and its current AO system, a next-generation AO system mounted on the W. M. Keck telescope (KNGAO), and the Thirty Meter Telescope (TMT) equipped with its AO system (NFIRAOS). The spatial resolution on the center of Io provided by these AO systems is respectively 140 km, 110 km and 35 km in the H band (1.6 microns). Two young eruptive centers labeled A & B can be detected only on the TMT observations. The KNGAO instrument detected the brightest eruption labeled A. Credit: F. Marchis
According to the team, observations reveal a series of young and energetic eruptions called outbursts. These events stand out indicating a high eruption temperature. Coincidentally, the team observed the awakening of the volcano Tvashtar while New Horizons slingshot past Jupiter on its way to Pluto. The eruption lasted from April 2006 to September 2007. Older observations from Galileo show a similar eruption pattern in 1999 lasting for 15 months.
“The episodicity of these volcanoes points to a regular recharge of magma storage chambers” said Ashley Davies a volcanologist at the Jet Propulsion Laboratory, California Institute of Technology, and a member of the study. “This will allow us to model the eruption process and understand the how heat is removed from Io’s deep interior by this particular style of volcanic activity.”
The team found four additional eruptions including a previously unobserved active volcano in 2004. The new sporadic blast accounted for about 10 percent of Io’s average thermal output, according to Marchis. The outburst was more energetic than Tvashtar in 2001. While the team continues to study Io, they have noted that since September 2010, the crazily active moon has been mostly quiet. A dozen or so permanent, low temperature eruptions dot the globe but the team has not detected the young, fire fountain style eruptions seen before.
“The next giant leap in the field of planetary astronomy is the arrival of Giant Segmented Mirror Telescopes, such as the Thirty Meter Telescope expected to be available in 2021. It will provide a spatial resolution of 35 km in the near-infrared, equivalent to the spatial resolution of global observations taken by the Galileo spacecraft. When pointed at Io, these telescopes will offer the equivalent of a spacecraft flyby of the satellite,” Marchis said.
Don Perovich, part of the ICESCAPE mission used a spectroradiometer to measure the amount of sunlight reflected from the surface of ice and melt ponds in the Chukchi Sea. Credit: NASA/Kathryn Hansen
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Imagine finding a rainforest in the middle of a desert. That is how NASA scientists are equating a new biological discovery in Arctic Ocean. Microscopic plants called phytoplankton are actively growing under the thinning Arctic ice. In fact, the scientists say the phytoplankton growth in the Arctic may now be richer than any other ocean region on Earth. The finding reveals a new consequence of the Arctic’s warming climate, and gives researchers an important clue to understanding the impacts of a changing climate and environment on the Arctic Ocean and its ecology.
“If someone had asked me before the expedition whether we would see under-ice blooms, I would have told them it was impossible,” said Kevin Arrigo of Stanford University, leader of the ICESCAPE mission and lead author of the new study. “This discovery was a complete surprise.”
ICESCAPE, stand for Impacts of Climate on EcoSystems and Chemistry of the Arctic Pacific Environment and in 2010 and 2011, scientists explored Arctic waters in the Beaufort and Chukchi seas along Alaska’s western and northern coasts onboard a U.S. Coast Guard icebreaker. The researchers drilled down through three-foot thick sea ice to study impacts of environmental variability and change in the Arctic on the ocean biology, ecology and biogeochemistry.
The researchers found the phytoplankton were extremely active, doubling in number more than once a day. Conversely, blooms in open waters grow at a much slower rate, doubling in two to three days. These growth rates are among the highest ever measured for polar waters.
Phytoplankton were thought to grow in the Arctic Ocean only after sea ice had retreated for the summer.
In July of 2011 the researchers observed blooms beneath the ice that extended from the sea-ice edge to 72 miles into the ice pack. Ocean current data revealed that these blooms developed under the ice and had not drifted there from open water, where phytoplankton concentrations can be high.
Previously, it was thought that sea ice blocked most sunlight needed for phytoplankton growth. Scientists now think that the thinning Arctic ice is allowing sunlight to reach the waters under the sea ice, spurring plant blooms where they had never been observed. The findings were published today in the journal Science.
Phytoplankton is the base of the marine food chain and they consume large amounts of carbon dioxide. Scientists will have to reassess the amount of carbon dioxide entering the Arctic Ocean through biological activity if the under-ice blooms turn out to be common.
“At this point we don’t know whether these rich phytoplankton blooms have been happening in the Arctic for a long time and we just haven’t observed them before,” Arrigo said. “These blooms could become more widespread in the future, however, if the Arctic sea ice cover continues to thin.”
The discovery of these previously unknown under-ice blooms also has implications for the broader Arctic ecosystem, including migratory species such as whales and birds. Phytoplankton are eaten by small ocean animals, which are eaten by larger fish and ocean animals. A change in the timeline of the blooms can cause disruptions for larger animals that feed either on phytoplankton or on the creatures that eat these microorganisms.
“It could make it harder and harder for migratory species to time their life cycles to be in the Arctic when the bloom is at its peak,” Arrigo said. “If their food supply is coming earlier, they might be missing the boat.”
The scientists said the discovery also may have major implications for the global carbon cycle and the ocean’s energy balance, and they may need to revise their understanding of the ecology of the Arctic and the region’s role in the Earth system.
Artist's rendering of an Earth-sized rogue planet approaching a star. Credit: Christine Pulliam (CfA)
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Free-floating “rogue” planets may occasionally dip into the inner Solar System, picking up dust containing organic compounds — a.k.a. the ingredients for life — and carry it back out into the galaxy, according to new research by Professor Chandra Wickramasinghe, Director of the University of Buckingham Centre for Astrobiology in the UK.
Rogue planets are thus called because they are not in orbit around a star. Either forcibly ejected from a solar system or having formed very early on in the Universe — even within a few million years after the Big Bang, the team proposes — these vagrant worlds may vastly outnumber stars. In fact, it’s been suggested there are as much as 100,000 times more rogue planets than stars in our Milky Way galaxy alone!
Professor Wickramasinghe — a proponent of the panspermia hypothesis whereby the ingredients for life can be transported throughout the galaxy on dust, comets, and perhaps even planets — and his team have suggested in a paper published in the journal Astrophysics and Space Science that Earth-sized rogue planets could pass through the inner Solar System, possibly as often as once every 25 million years on average. Like a cosmic drive-thru these planets could gather zodiacal dust from the plane of the Solar System during their pass, thus picking up organic compounds along the way.
The planets would then take the material gathered from one solar system and possibly bring it into another, serving as a type of interstellar cross-pollinator.
Wickramasinghe’s team propose that, by this process, there could be more life-bearing, Earth-sized planets existing between the stars than orbiting around them — a lot more. Based on their estimates there may be as much as a few hundred thousand billion such worlds in our galaxy… that’s several thousand for every star.
It will be interesting to see how this idea is received, but it definitely is an intriguing concept. As we hunt for the “Holy Grail” of life-friendly exoplanets around other stars, they may be drifting through the darkness in number, hiding in the spaces between.
In this artist's conception, a rogue planet drifts through space. Credit: Christine Pulliam (CfA)
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As crazy as it sounds, free-floating rogue planets have been predicted to exist for quite some time and just last year, in May 2011, several orphan worlds were finally detected. Then, earlier this year, astronomers estimated that there could be 100,000 times more rogue planets in the Milky Way than stars. Now, the latest research suggests that sometimes, these rogue, nomadic worlds can find a new home by being captured into orbit around other stars. Scientists say this finding could explain the existence of some planets that orbit surprisingly far from their stars, and even the existence of a double-planet system.
“Stars trade planets just like baseball teams trade players,” said Hagai Perets of the Harvard-Smithsonian Center for Astrophysics.
Astronomers now understand that rogue planets are a natural consequence of both star and planetary formation. Newborn star systems often contain multiple planets, and if two planets interact, one can be ejected in a form of planetary billiards, kicked out of the star system to become an interstellar traveler.
But later, if a rogue planet encounters a different star moving in the same direction at the same speed, be captured into orbit around that star, say Perets and Thijs Kouwenhoven of Peking University, China, the authors of a new paper in The Astrophysical Journal.
A captured planet tends to end up hundreds or thousands of times farther from its star than Earth is from the Sun. It’s also likely to have a, orbit that’s tilted relative to any native planets, and may even revolve around its star backward.
Perets and Kouwenhoven simulated young star clusters containing free-floating planets. They found that if the number of rogue planets equaled the number of stars, then 3 to 6 percent of the stars would grab a planet over time. The more massive a star, the more likely it is to snag a planet drifting by.
While there haven’t actually been planets found yet that are definitely a ‘captured’ world, the best bet would perhaps be a planet in a distant orbit around a low-mass star. The star’s disk wouldn’t contain enough material to form a planet that distant, Perets and Kouwenhoven said.
The best evidence of a captured planet comes from the European Southern Observatory, which announced in 2006 the discovery of two planets (weighing 14 and 7 times Jupiter) orbiting each other without a star.
“The rogue double-planet system is the closest thing we have to a ‘smoking gun’ right now,” said Perets. “To get more proof, we’ll have to build up statistics by studying a lot of planetary systems.”
As for our own solar system, there’s no evidence at this time that our Sun could have captured an alien world, which would lie far beyond Pluto.
“There’s no evidence that the Sun captured a planet,” said Perets. “We can rule out large planets. But there’s a non-zero chance that a small world might lurk on the fringes of our solar system.”
Newly detected series of narrow linear troughs are known as graben, and they formed in highland materials on the lunar farside. These graben are located on a topographic rise with several hundred meters of relief revealed in topography derived from Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) stereo images (blues are lower elevations and reds are higher elevations). Image Credit: NASA/GSFC/Arizona State University/Smithsonian Institution
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Recent images from NASA’s Lunar Reconnaissance Orbiter Camera provide evidence that the lunar crust may be pulling apart in certain areas. The images reveal small trenches less than a kilometer in length, and less than a few hundred meters wide. Only a small number of these features, known as graben, have been discovered on the lunar surface.
There are several clues in the high-resolution images that provide evidence for recent geologic activity on the Moon.
The LROC team detected signs of contraction on the lunar surface as early as August of 2010. The contractions were in the form of lobe-shaped ridges known as lobate scarps. Based on the data, the team suggests the widely-distributed scarps indicate the Moon shrank in diameter, and may be continuing to shrink. Interestingly enough, the new image data featuring graben presents a contradiction, as they indicate lunar crust being pulled apart and theorize that the process that created the graben may have occurred within the past 50 million years.
“We think the Moon is in a general state of global contraction due to cooling of a still hot interior, said thomas Watters from the Center for Earth and Planetary Studies. “The graben tell us that forces acting to shrink the Moon were overcome in places by forces acting to pull it apart. This means the contractional forces shrinking the Moon cannot be large, or the small graben might never form.”
Based on the size of the graben, the forces responsible for contraction of the lunar surface are assumed to be fairly weak. It is further theorized that, unlike the early terrestrial planets, the Moon was not completely molten during its early history.
“It was a big surprise when I spotted graben in the farside highlands,” said Mark Robinson, LROC Principal Investigator at Arizona State University. “I immediately targeted the area for high resolution stereo images so we could create a 3-dimensional view of the graben. It’s exciting when you discover something totally unexpected. Only about half the lunar surface has been imaged in high resolution. There is much more of the Moon to be explored.”
If you’d like to learn more about the recently discovered graben on the moon, you can watch a short video by Thomas Watters below:
The Death Star. Image Credit: Wookieepedia / Lucasfilm
[/caption]Countless Sci-Fi fans vividly remember the famous scene in Star Wars in which the Death Star obliterates the planet Alderaan.
Mirroring many late night caffeine-fueled arguments among Sci-Fi fans, a University of Leicester researcher asks the question:
Could a small moon-sized battle station generate enough energy to destroy an Earth-sized planet?
A paper by David Boulderston (University of Leicester) sets out to answer that very question. First, for the uninitiated, just what the heck is a Death Star?
According to Star Wars lore, the DS-1 Orbital Battle Station, or Death Star, is a moon-sized battle station designed to spread fear throughout the galaxy. The image above shows the Death Star as it appeared in Star Wars Episode IV: A New Hope (1977). The Death Star’s main weapon is depicted as a superlaser capable of destroying planets with a single blast.
Boulderston claims that it is possible to estimate how much energy the Death Star would need in order to destroy a planet with its superlaser. There are a number of assumptions made, however, in order to come up with the energy requirement.
For starters, Boulderston assumed that Alderaan did not have any sort of planetary “deflector” shield. A second assumption is that the planet is a solid body of uniform density – essentially ignoring the complex interior of planets, due to lack of information on Alderaan itself. Using the idealized sphere model based on Earth’s mass and diameter, it was possible to determine the gravitational binding energy of Alderaan, using a simple equation of:
U= 3GMp2
——
5Rp
Where G is the Gravitational Constant (6.673×10-11), Mp is planet mass, and Rp is the planet’s radius. Using Earth’s mass and radius, the required energy comes out to 2.25 x 1032 Joules. Using Jupiter’s data, the energy required goes up to 2 x 1036 Joules.
Boulderston asserts that (according to Star Wars lore) the Death Star is powered by a ‘hypermatter’ reactor, possessing the energy output of several main-sequence stars. Given that the power output of our Sun is about 3 x 1026 Joules per second, it’s a reasonable assumption the Death Star’s reactor could power the superlaser.
Despite using a simplified model of a planet, Boulderstone states the simplified model is reasonable to use since the Death Star’s main power reactor has the energy output equal to several main-sequence stars. Even if Earth’s exact composition were used in the equation above, the required energy to destroy a planet would only be affected by a few orders of magnitude – well within the Death Star’s power budget.
Boulderstone reiterated that the energy required to destroy a Jupiter-sized planet would put considerable strain on the Death Star. To destroy a planet like Jupiter, all power from essential systems and life support (no re-routing from the auxiliary EPS conduits – that’s a Star Trek hack!) would be required, which is not necessarily possible.
Boulderstone’s conclusion is that the Death Star could indeed destroy Earth-like planets, given its main power source. While the Death Star could destroy an Earth-sized planet, a Jupiter-sized planet would be a tough challenge, and the Galactic Empire would need to resort to using a Suncrusher to destroy stars.
The search for extraterrestrial life outside our Solar System is currently focused on extrasolar planets within the ‘habitable zones’ of exoplanetary systems around stars similar to the Sun. Finding Earth-like planets around other stars is the primary goal of NASA’s Kepler Mission.
The habitable zone (HZ) around a star is defined as the range of distances over which liquid water could exist on the surface of a terrestrial planet, given a dense enough atmosphere. Terrestrial planets are generally defined as rocky and similar to Earth in size and mass. A visualization of the habitable zones around stars of different diameters and brightness and temperature is shown here. The red region is too hot, the blue region is too cold, but the green region is just right for liquid water. Because it can be described this way, the HZ is also referred to as the “Goldilocks Zone”.
Normally, we think of planets around other stars as being similar to our solar system, where a retinue of planets orbits a single star. Although theoretically possible, scientists debated whether or not planets would ever be found around pairs of stars or multiple star systems. Then, in September, 2011, researchers at NASA’s Kepler mission announced the discovery of Kepler-16b, a cold, gaseous, Saturn-sized planet that orbits a pair of stars, like Star Wars’ fictional Tatooine.
This week I had the chance to interview one of the young guns studying exoplanets, Billy Quarles. Monday, Billy and his co-authors, professor Zdzislaw Musielak and associate professor Manfred Cuntz, presented their findings on the possibility of Earth-like planets inside the habitable zones of Kepler 16 and other circumbinary star systems, at the AAS meeting in Austin, Texas.
The Goldilocks Zones around various type stars. Credit: NASA/JPL-Caltech
“To define the habitable zone we calculate the amount of flux that is incident on an object at a given distance,” Billy explained. “We also took into account that different planets with different atmospheres will retain heat differently. A planet with a really weak greenhouse effect can be closer in to the stars. For a planet with a much stronger greenhouse effect, the habitable zone will be further out.”
“In our particular study, we have a planet orbiting two stars. One of the stars is much brighter than the other. So much brighter, that we ignored the flux coming from the smaller fainter companion star altogether. So our definition of the habitable zone in this case is a conservative estimate.”
Quarles and his colleagues performed extensive numerical studies on the long-term stability of planetary orbits within the Kepler 16 HZ. “The stability of the planetary orbit depends on the distance from the binary stars,” said Quarles. “The further out the more stable they tend to be, because there is less perturbation from the secondary star.”
For the Kepler 16 system, planetary orbits around the primary star are only stable out to 0.0675 AU (astronomical units). “That is well inside the inner limit of habitability, where the runaway greenhouse effect takes over,” Billy explained. This all but rules out the possibility of habitable planets in close orbit around the primary star of the pair. What they found was that orbits in the Goldilocks Zone farther out, around the pair of Kepler 16’s low-mass stars, are stable on time scales of a million years or more, providing the possibility that life could evolve on a planet within that HZ.
Kepler 16's orbit from Quarles et al
Kepler 16b’s roughly circular orbit, about 65 million miles from the stars, is on the outer edge of this habitable zone. Being a gas giant, 16b is not a habitable terrestrial planet. However, an Earth-like moon, a Goldilocks Moon, in orbit around this planet could sustain life if it were massive enough to retain an Earth-like atmosphere. “We determined that a habitable exomoon is possible in orbit around Kepler-16b,” Quarles said.
I asked Quarles how stellar evolution impacts these Goldilocks Zones. He told me, “There are a number of things to consider over the lifetime of a system. One of them is how the star evolves over time. In most cases the habitable zone starts out close and then slowly drifts out.”
During a star’s main sequence lifetime, nuclear burning of hydrogen builds up helium in its core, causing an increase in pressure and temperature. This occurs more rapidly in stars that are more massive and lower in metallicity. These changes affect the outer regions of the star, which results in a steady increase in luminosity and effective temperature. The star becomes more luminous, causing the HZ to move outwards. This movement could result in a planet within the HZ at the beginning of a star’s main sequence lifetime, to become too hot, and eventually, uninhabitable. Similarly, an inhospitable planet originally outside the HZ, may thaw out and enable life to commence.
“For our study, we ignored the stellar evolution part,” said lead author, Quarles. “We ran our models for a million years to see where the habitable zone was for that part of the star’s life cycle.”
Being at the right distance from its star is only one of the necessary conditions required for a planet to be habitable. Habitable conditions on a planet require various geophysical and geochemical conditions. Many factors can prevent, or impede, habitability. For example, the planet may lack water, gravity may be too weak to retain a dense atmosphere, the rate of large impacts may be too high, or the minimum ingredients necessary for life (still up for debate) may not be there.
One thing is clear. Even with all the requirements for life as we know it, there appear to be plenty of planets around other stars, and very likely, Goldilocks Moons around planets, orbiting within the habitable zones of stars in our galaxy, that detecting the signature of life in the atmosphere of a planet or moon around another Sun seems like only a matter of time now.
NASA’s Kepler mission has detected no shortage of planets; more than a thousand candidates were discovered in 2011, a handful of which were Earth-like in size. As data from the mission keeps pouring in, astronomers are continuing to confirm and classify these possible exoplanets. Today, a team of astronomers from the California Institute of Technology added three more to the growing list. They have confirmed the three smallest exoplanets yet discovered.
Kepler searches for planets by looking at stars. The light from the star flickers or dips when a planet passes in front of it. At least three passes are required to confirm that the signal is from a planet, and further ground-based observations are necessary before a discovery can be confirmed.
An artist's impression of Kepler's field of view, the area in which it is constantly searching for new planets. Image Credit: Jon Lomberg/NASA
The Cal Tech team’s discovery was made with old data from Kepler. They found that the three planets are rocky like Earth and orbit a single star called KOI-961. They are also smaller than our planet; their radii are 0.78, 0.73 and 0.57 times that of Earth. As a comparison, the smallest of the three is roughly the size of Mars.
That these planets are so small is big news; they were thought to be much bigger when they were first found. Finding a planet as small as Mars is particularly amazing, said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. It “hints that there may be a bounty of rocky planets all around us.”
The whole system is also small. The planets orbit so close to their star that their year lasts only two days. “This is the tiniest solar system found so far,” said John Johnson, the principal investigator of the research from NASA’s Exoplanet Science Institute at Cal Tech in Pasadena.
A view of Kepler's search area as seen from Earth. Image credit: Carter Roberts / Eastbay Astronomical Society
Their star, KOI-961, is a red dwarf with a diameter one-sixth that of our Sun and it is only 70 percent larger than Jupiter. This makes the system’s scale much closer to that of Jupiter and its moons than that of the Sun and the planets in our Solar System. As Johnson explains, this speaks to “the diversity of planetary systems in our galaxy.”
The type of star is also significant. Red dwarfs are the most common stars in the Milky Way galaxy, and the discovery of three rocky planets around one suggests that the galaxy could be teeming with similar rocky planets.
The team’s find, however, isn’t going to provide us with intergalactic vacation homes anytime soon. The planets are all too close to their star to be in the habitable zone, an orbit where water can exist as a liquid on the surface. Nevertheless, the tiny planets are a significant find. “These types of systems could be ubiquitous in the universe,” said Phil Muirhead, lead author of the new study from Caltech. “This is a really exciting time for planet hunters.”
This was even selected by Scientific American as one of the Top 5 Space Stories of 2012.
