A global view of Mercury, as seen by MESSENGER. Credit: NASA
Three to two. That’s the ratio of the time it takes Mercury to go around the sun (88 days) in relation to its rotation (58 days). This is likely due to the influence of the Sun’s immense gravity on the planet. A new study confirms that finding, while stating something even more interesting: other star systems could see the same type of resonance.
Hundreds of confirmed exoplanets have been found so far, many of them in very tight configurations, the authors said. “Mercury-like states should be common among the hundreds of discovered and confirmed exoplanets, including potentially habitable super-Earths orbiting M-dwarf [red dwarf] stars,” they added. “The results of this investigation provide additional insight into the possibilities of known exoplanets to support extraterrestrial life.”
Habitability, of course, depends on many metrics. What kind of star is in the system, and how stable is it? How far away are the planets from the star? What is the atmosphere of the planet like? And as this study points out, what about if one side of the planet is tidally locked to its star and spends most or all of its time with one side facing the starshine?
Additionally, the study came up with an explanation as to why Mercury remains in a 3:2 orbit in opposition to, say, the Moon, which always has one side facing the Earth. The study took into account factors such as internal friction and a tidal “bulge” that makes Mercury appear slightly misshapen (and which could slow it down even further.) Basically, it has to do with Mercury’s early history.
From Orbit, Looking toward Mercury’s Horizon. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
“Among the implications of the released study are, to name a few, a fast tidal spin-down, a relatively cold (i.e., not fully molten) state of the planet at the early stages of its life, and a possibility that the internal segregation and formation of the massive liquid core happened after Mercury’s capture into the resonance,” the press release added.
The results were presented today (Oct. 7) at the American Astronomical Society department of planetary sciences meeting held in Denver. A press release did not make clear if the study has been submitted for peer review or published.
Cloud map of Kepler-7b (left) in comparison to Jupiter (right). Credit: NASA/JPL-Caltech/MIT
Call it cloudy with a low chance of meatballs. The alien world Kepler-7b — a very reflective world in big telescopes — has clouds in its upper atmosphere. And scientists have actually been able to map those out, despite the planet’s great distance from Earth (at least 1,000 light-years away.)
It’s the first time scientists have been able to map out clouds on a world outside of the solar system. If we can see clouds, then we can begin to think about what a planet’s climate will be, making this an important milestone in understanding the conditions on other worlds.
“Kepler-7b reflects much more light than most giant planets we’ve found, which we attribute to clouds in the upper atmosphere,” stated Thomas Barclay, Kepler scientist at NASA’s Ames Research Center. “Unlike those on Earth, the cloud patterns on this planet do not seem to change much over time — it has a remarkably stable climate.”
Illustration of the Kepler spacecraft (NASA/Kepler mission/Wendy Stenzel)
Here’s how scientists got it done:
Preliminary observations with the Kepler space telescope –which was designed to hunt planets until a second reaction wheel failed earlier this year — found “moon-like phases” on Kepler-7b. These showed a bright spot on the western hemisphere.
NASA’s Spitzer Space Telescope measured Kepler-7b’s temperature using infrared light, calculating it at between 1,500 and 1,800 degrees Fahrenheit (815 and 982 degrees Celsius.)
Something was clearly going on, as the planet is extremely close to its star; only 0.06 Earth-sun distances away. The temperature was too cool. They figured out that the light was reflected off cloud tops on the planet’s west side.
Another cool fact — Kepler-7b, like Saturn, would float if it was put in a big enough tub of water!
You can read more details in the technical paper online here. The study, which was led by the Massachusetts Institute of Technology, has been accepted to the Astrophysical Journal, but not published yet.
Artist's conception of an Earth-like exomoon orbiting a gaseous planet. Image credit: Avatar, 20th Century Fox
Astronomers believe that hidden deep within the wealth of data collected by NASA’s Kepler mission are minuscule signatures confirming the presence of exomoons. With such a promising discovery on the horizon, researchers are beginning to address the factors that may deem these alien moons habitable.
A new study led by Dr. René Heller from McMaster University in Canada and Dr. Jorge Zuluaga from the University of Antioquia in Colombia takes a theoretical look at habitability – exploring the key components that may make exomoons livable. While stellar and planetary heating play a large role, it’s quickly becoming clear that the magnetic environments of exomoons may be even more critical.
An exoplanet’s habitability is first and foremost based on the circumstellar habitable zone – the temperature band around a star in which water may exist in its liquid state. Exomoons, however, have an additional set of constraints that affect their habitability. In a set of recent papers, Dr. Heller and Dr. Rory Barnes (from the University of Washington) defined a “circumplanetary habitable edge,” which is roughly analogous to the circumstellar habitable zone.
Here the question of habitability is based on the relationship between the exomoon and its host planet. The additional energy source from the planet’s reflected starlight, the planet’s thermal emission, and tidal heating in the moon may create a runaway greenhouse effect, rendering the exomoon uninhabitable.
One look at Io – Jupiter’s closest Galilean satellite – shows the drastic effects a nearby planet may have on its moon. The strong gravitational pull of Jupiter distorts Io into an ellipsoid, whose orbit around the giant planet is eccentric due to perturbations from the other Galilean moons. As the orbital distance between Jupiter and Io varies on an eccentric orbit, Io’s ellipsoidal shape oscillates, which generates enormous tidal friction. This effect has led to over 400 active volcanic regions.
Note that this is an edge, not a zone. It defines only an innermost habitable orbit, inside which a moon would become uninhabitable. The exomoon must exist outside this edge in order to avoid intense planetary illumination or tidal heating. Exomoons situated in distant orbits, well outside the circumplanetary habitable edge, have a chance at sustaining life.
But the question of habitability doesn’t end here. Harmful space radiation can cause the atmosphere of a terrestrial world to be stripped off. Planets and moons rely heavily on magnetic fields to act as protective bubbles, preventing harmful space radiation from depleting their atmospheres.
With this in mind, Heller and Zuluaga set out to understand the evolution of magnetic fields of extrasolar giants, which are thought to affect their moons. It’s unlikely that small, Mars-sized exomoons will produce their own magnetic fields. Instead, they may have to rely on an extended magnetic field from their host planets.
This planetary magnetosphere is created by the shock between the stellar wind and the intrinsic magnetic field of the planet. It has the potential to be huge, protecting moons in very distant orbits. Within our own Solar System Jupiter’s magnetosphere ends at distances up to 50 times the size of the planet itself.
Heller and Zuluaga computed the evolution of the extent of a planetary magnetosphere. “Essentially, as the pressure of the stellar wind decreases over time, the planetary magnetic shield expands,” Dr. Heller told Universe Today. “In other words, the planetary magnetosphere widens over time.”
Evolution of the host planets magnetosphere (represented by the blue line) for Neptune-, Saturn-, and Jupiter-like planets. All increase over time by a varying amount.
The team applied these two models to three scenarios: Mars-sized moons orbiting Neptune-, Saturn-, and Jupiter-like planets. These three systems were always located in the center of the circumstellar habitable zone of a 0.7 solar-mass star. Here are the take-home messages:
1.) Mars-like exomoons beyond 20 planetary radii around any of the three host planets act like free planets around a star. They are well outside the habitable edge, experiencing no significant tidal heating or illumination. While their extreme distance is promising, they will never be enveloped within their host planet’s magnetosphere and are therefore unlikely to harbor life.
2.) Mars-like exomoons between 5 and 20 planetary radii face a range of possibilities. “Intriguingly, formation theory and observations of moons in the Solar System tell us that this is the range in which we should expect most exomoons to reside,” explains Dr. Heller.
For an exomoon beyond the habitable edge of a Neptune-like planet it may take more than the age of the Earth, that is, 4.6 billion years to become embedded within its host planet’s magnetosphere. For a Saturn-like planet it may take even longer, but for a Jupiter-like planet it will take less than 4.3 billion years.
3.) Mars-like exomoons inside 5 planetary radii are enveloped within the planetary magnetosphere early on but not habitable as they orbit within the planet’s habitable edge.
In order for an exomoon to be habitable it must exist well outside the habitable edge, safe from stellar and planetary illumination as well as tidal heating. But at the same time it must also exist near enough to its host planet to be embedded within the planet’s magnetosphere. The question of habitability depends on a delicate balance.
Dr. Zuluaga stressed that “one of the key consequences of this initial work is that although magnetic fields have been recognized as important factors determining the habitability of terrestrial planets across the Universe, including the Earth, Mars, and Venus, in the case of moons, the magnetic environment could be even more critical at defining the capacity of those worlds to harbor life.”
The paper has been accepted for publication in the Astrophysical Journal Letters and is available for download here.
Artist's concept of NASA's Spitzer Space Telescope surrounded by examples of exoplanets it has looked at. Credit: NASA/JPL-Caltech
After 10 years in space — looking at so many galaxies and stars and other astronomy features — the Spitzer Space Telescope is being deployed for new work: searching for alien worlds.
The telescope is designed to peer in infrared light (see these examples!), the wavelength in which heat is visible. When looking at infrared light from exoplanets, Spitzer can figure out more about their atmospheric conditions. Over time, it can even detect brightness differences as the planet orbits its sun, or measure the temperature by looking at how much the brightness declines when the planet goes behind its star. Neat stuff overall.
“When Spitzer launched back in 2003, the idea that we would use it to study exoplanets was so crazy that no one considered it,” stated Sean Carey of NASA’s Spitzer Science Center, which is at the California Institute of Technology. “But now the exoplanet science work has become a cornerstone of what we do with the telescope.”
Of course, the telescope wasn’t designed to do this. But to paraphrase the movie Apollo 13, NASA was interested in what the telescope could do while it’s in space — especially because the planet-seeking Kepler space telescope has been sidelined by a reaction wheel problem. Redesigning Spitzer, in a sense, took three steps.
An example of Spitzer’s past work: This image from NASA’s Spitzer Space Telescope shows infrared light from the Sunflower galaxy, otherwise known as Messier 63. Spitzer’s view highlights the galaxy’s dusty spiral arms. Image credit: NASA/JPL-Caltech
Fixing the wobble: Spitzer is steady, but not so steady that it could easily pick out the small bit of light that an exoplanet emits. Engineers determined that the telescope actually wobbled regularly and would wobble for an hour. Looking into the problem further, they discovered it’s because a heater turns on to keep the telescope battery’s temperature regulated.
“The heater caused a strut between the star trackers and telescope to flex a bit, making the position of the telescope wobble compared to the stars being tracked,” NASA stated. In October 2010, NASA decided to cut the heating back to 30 minutes because the battery only needs about 50 per cent of the heat previously thought. Half the wobble and more exoplanets was more the recipe they were looking for.
The Spitzer Space Telescope. Credit: NASA
Repurposing a camera: Spitzer has a pointing control reference sensor “peak-up” camera on board, which originally gathered up infrared light to funnel to a spectrometer. It also calibrated the telescope’s star-tracker pointing devices. The same principle was applied to infrared camera observations, putting stars in the center of camera pixels and allowing a better view.
Remapping a camera pixel: The scientists charted the variations in a single pixel of the camera that showed them which were the most stable areas for observations. For context, about 90% of Spitzer’s exoplanet observations are about a 1/4 of a pixel wide.
That’s pretty neat stuff considering that Spitzer’s original mission was just 2.5 years, when it had coolant on board to allow three temperature-sensitive science instruments to function. Since then, engineers have set up a passive cooling system that lets one set of infrared cameras keep working.
An artist's conception of a disintegrating planet - creating a trail of dust - around its rocky star.
Solar flares – huge eruptions of charged particles from the Sun – present little threat to Earth. On a few rare occasions these particles may disrupt our communications systems and cause radio blackouts. But they tend to be more aesthetically pleasing than harmful. It’s certainly a sight to be seen as these energetic particles collide with our atmosphere, resulting in a cascade of colorful lights – the aurora borealis.
Fortunately our planet provides the protection necessary from such harmful space radiation. But not all planets are quite so lucky. Take for instance Kepler’s latest object of interest: KIC 12557548b, a super Mercury-size planet candidate. Astronomers have recently found that due to this star’s activity – producing massive stellar flares – the planet itself is evaporating.
Only last year, four different sources published evidence that this rocky planet was disintegrating. Thanks to Kepler, it quickly became clear that the total amount of light from KIC 12557548 as a function of time – the light curve of the system – dropped every 15.7 hours as a planet orbited it. But the amount of light blocked due to the transiting planet varied from 0.2% to more than 1.2%.
The amount of light blocked is dependent on the size of the planet. A Jupiter-size planet will block more light than a Mercury-size planet. The variations here suggest a range for the size of the planet: from a super Mercury-sized planet to a Jupiter-sized planet.
But this wasn’t the planet’s only enigma. It also has an asymmetric light curve. The total light from the star drops steadily as the planet begins its transit, plateaus as the planet fully covers the disk of the star, and then increases as the planet ends its transit. But the rate at which the light drops is much faster than the rate at which it increases. It takes longer for the light curve to return to its original brightness, hinting at a tail of debris that trails the planet, continuing to block light.
The light curves of KIC 12557548b. The left-hand plot represents deep transits, whereas the right-hand plot represents more shallow transits. Both plots show a clear asymmetry. Source: Brogi et al. 2012
It appears that the planet is evaporating – emitting small particles of dust into orbit, which then trails behind it. The varying transit depth reflects the amount of dust currently evaporating.
Recently a team from the University of Tokyo analyzed the system in more detail, attempting to explain why this tiny planet is evaporating. “We found that the transit depth negatively correlates with the modulation of the stellar flux,” Dr. Kawahara, lead author on the study, told Universe Today. “The dust amount increases when the planet is located in front of the star spots.”
The transit depth does not vary randomly, but every 22.83 days. This coincides with the modulation of the stellar flux, or simply the stellar rotation period. Star spots may be indirectly detected by a star’s noticeable decrease in stellar flux. Because these star spots are large (much larger than sunspots) they last for long periods of time, and may be used to deduce the star’s rotation period.
Kawahara et al. found that the transit depth periodically varies with the stellar rotation rate – finding a correlation between stellar activity and the rate at which the planet is evaporating.
“Energy from the star spots increases the amount of dust and atmosphere from the planet,” explains Dr. Kawahara. The extreme heat and wind is enough to speed up the motions of the dust molecules; making them fast enough to escape the planet’s gravitational pull.
Future spectroscopic studies may search for molecules in the evaporating atmosphere of KIC 12557548b. But Dr. Kawahara remarks that due to the planet’s faintness it is unlikely. His best hope is that future studies may instead find a similar object closer to us, that may be more easy to study.
The finding is published in The Astrophysical Journal Letters and is available for download here.
Artist's conception of the alien planet system orbiting Gliese 581. Credit: ESO/L. Calçada
One big challenge in astronomy is everything is so darn far away. This makes it hard to see the signs of life in planets, which are usually but tiny dots of light using the telescope technology we have today.
There are signs in Earth’s atmosphere that life is on the surface — methane from microbes, for example — and already scientists have years of research concerning ideas to find “biomarkers” on other planets. A new model focuses on a theoretical Earth-sized planet orbiting a red dwarf star, where it is believed biomarkers would be easier to find because these stars are smaller and fainter than that of the sun.
“We developed computer models of exoplanets which simulate the abundances of different biomarkers and the way they affect the light shining through a planet’s atmosphere,” stated Lee Grenfell, who is with the German Aerospace Center (DLR) institute of planetary science.
Preliminary work has already been done to find chemicals in the planet’s atmosphere (by looking at how they affect light that pass through the chemicals) particularly on large exoplanets that are close to their star (sometimes called “hot Jupiters“). Signs of life would be found through a similar process, but would be much fainter.
Artist’s impression of a red dwarf (courtesy NASA)
The research team constructed a model of a planet similar to Earth, at different orbits and distances from a red dwarf stars. Their work shows a sort of “Goldilocks” effect (or, a condition that is “just right”) to find ozone when the ultraviolet radiation falls into the medium of a given range. If it is too high, the UV heats the middle atmosphere and obliterates the biomarker signal. Too low UV makes the signal very hard to find.
“We find that variations in the UV emissions of red-dwarf stars have a potentially large impact on atmospheric biosignatures in simulations of Earth-like exoplanets. Our work emphasizes the need for future missions to characterise the UV emissions of this type of star,” said Grenfell.
The research has plenty of limitations, he added. We don’t know what alien life would look like, we don’t know if planets near red dwarfs are a good place to search, and even if we found a signal that looked like life, it could have come from another process. Still, Grenfell’s team expects the model is a good basis on which to continue asking the question: is life really out there?
The research has been submitted to the journal Planetary and Space Science.
Determining weather patterns in exoplanet atmospheres – hundreds to thousands of light years away – is extremely difficult. However, given that it may be one of our best ways to truly characterize these alien words, it’s a challenge astronomers have accepted willingly.
Most models have a very simple foundation, necessarily eliminating the complex physics that is difficult to incorporate and analyze. Recently, a team led by Dr. Konstantin Batygin of Harvard University, added one more parameter to their models, drastically changing their results.
The punch line is this: the inclusion of magnetic fields significantly changes, and actually simplifies, the atmospheric circulation of hot Jupiters.
Hot Jupiters orbit dangerously close to their host stars, roasting in stellar radiation. But they are also tidally locked to their host stars – one hemisphere continually faces the star, while one continuously faces away – creating a permanent dayside and a permanent nightside.
One would expect the temperature gradient between the dayside and the nightside to be very high. However, various weather patterns play a role in strongly decreasing this temperature gradient. As an example, we now know that clouds may significantly decrease the temperature of the dayside.
Dr. Batygin’s team analyzed magnetic effects within atmospheric circulation. “The case of hot Jupiters is quite peculiar,” she told Universe Today. “The atmospheres of hot Jupiters have temperatures that reach up to 2000 Kelvin, which is hot enough to ionize trace Alkali metals such as potassium and sodium. So the air on hot Jupiters is actually a weakly conducting plasma.”
Once the alkali metals have been ionized – stripped of their electrons – the upper atmosphere contains all of those charged particles and becomes a plasma. It is then electrically conductive and magnetic effects must be taken into account.
While the underlying physics is pretty complex (with nearly 40 multi-lined equations in the paper alone), the introduction of magnetic effects actually simplified the model’s outcome.
In the absence of magnetic fields, the upper and lower atmospheres feature two distinct patterns of circulation. The upper atmosphere consists of winds blowing away from the dayside in all directions. And the lower atmosphere consists of zonal flows – the bands of color on Jupiter. The zonal flows move parallel to lines of latitude in an east-west fashion. Each moves in a different direction than the one above and below it.
“Upon introducing magnetic fields, fancy dayside-to-nightside flows are quenched and the entire atmosphere circulates in an exclusively east-west fashion,” explains Dr. Batygin. The upper atmosphere resembles the lower atmosphere – zonal flows dominate.
Throughout these models, Dr. Batygin et al. assumed a magnetic field aligned with the rotation axis of the planet. Future work will include a closer look at the effect of a more complicated geometry. The team also intends to extend these results to hotter atmospheres, where magnetic fields will slow the rate of these zonal flows. According to Dr. Batygin, “this has potentially observable consequences and we hope to elucidate them in the future.”
These results will be published in the astrophysical journal (preprint available here).
Astronomers have found that tiny, round, dark clouds called globulettes have the right characteristics to form free-floating planets. The graph shows the spectrum of one of the globulettes taken at the 20-metre telescope at Onsala Space Observatory. Radio waves from molecules of carbon monoxide (13CO) give information on the mass and structure of these clouds. ESO/M. Mäkelä.
Free-floating rogue planets are intriguing objects. These planet-sized bodies adrift in interstellar space were predicted to exist in 1998, and since 2011 several orphan worlds have finally been detected. The leading theory on how these nomadic planets came to exist is that they were they ejected from their parent star system. But new research shows that there are places in interstellar space that might have the right conditions to form planets — with no parent star required.
Up until 20 years ago, the only planets astronomers were aware of were within our Solar System. They assumed others were out there, but none had ever been detected.
Today we know of almost a thousand planets orbiting other stars. They come in a wide variety of sizes. Some are smaller than Earth, and others are more massive than Jupiter. Some are found around solitary stars, while others are located in multiple star systems. In those systems, there can be individual or even multiple planets in orbit. In fact, recent surveys suggest there are planets orbiting every single star in the Milky Way.
So, what methods do astronomers use to find these “extrasolar planets”?
The first extrasolar planet was discovered in 1991.
It was found orbiting a pulsar, a dead star that rotates rapidly, firing out bursts of radiation on an eerily precise interval. As the planets orbit the pulsar, they pull it back and forth with their gravity. This slightly changes the wavelength of the radiation bursts streaming from the exotic star. Astronomers were able to measure these changes, and calculate the orbits of multiple planets.
Radial Velocity Method Extrasolar Planets Far Across GalaxyThe golden age of extrasolar planet discovery began in 1995 when a team from the University of Geneva discovered a planet orbiting the nearby star 51 Pegasi. Astronomers used spectroscopy to break up the light to reveal the elements in its stellar atmosphere. They carefully measured how the wavelengths of light were Doppler shifted over time, and used a technique known as the radial velocity method. They calculated the star’s average motion, and discovered slight variations, as if something was yanking the star towards and away from us.
That something, was a planet.
In fact, this planet was unlike anything we have in the Solar System. 51 Pegasi B has about half the mass of Jupiter and it orbits much closer to its parent star. Closer even, than Mercury to the Sun.
Until this discovery, astronomers didn’t think it was possible for planets to orbit this close, and have had to revise their theories on planetary formation. Many Hot Jupiter planets have been discovered since, some in even more extreme environments.
Gravitational Microlensing Gravitational microlensing method requires that you have two stars that lie on a straight line in relation to us here on Earth. Then the light from the background star is amplified by the gravity of the foreground star, which thus acts as a magnifying glass.Another method astronomers use to find planets is called gravitational microlensing. It works by carefully measuring the brightness of one star as it passes in front of another. The foreground star acts like a lens, focusing the light with its gravity and causing the star to brighten for a few hours. If the foreground star has planets, these will create a telltale spike in the light signature coming from the event.
Amateur astronomers around the world participate in microlensing studies, imaging stars quickly when an event is announced.
Transit Method Of course clouds are no issue if you’re watching the Transit of Venus from the ISS or the Hinode spacecraft. Compare this Hinode Transit image published on APOD on June 9 and enhanced by Marco Di Lorenzo,
The most successful way of finding planets is the transit method.
This is where telescopes measure the total amount of light coming from a star, and detect a slight variation in brightness as a planet passes in front.
Using this technique, NASA’s Kepler Mission has turned up thousands of candidate planets. Including some less massive than Earth, and others in the star’s habitable zone.
From the Kepler data, It’s just a matter of time before the holy grail of planets is uncovered… an Earth-sized world, orbiting a Sun-like star within the habitable zone.
All of these techniques are limited as they require the planets to be orbiting directly between us and their star. If the planets orbit above or below this plane, we just can’t detect them.
Coronographs New Worlds ImagerThere is another method in the works that would unleash the discovery of extrasolar planets, coronographs.
Imagine if you could block all the light from the star, and only see the planets in orbit. This technique has been used for observing the Sun’s atmosphere, but it requires much more precision to see distant stars.
One idea is to position a sunflower-shaped starshade in space, 125,000 km away from the observing telescope. This shade would just cover the star, dimming it by a factor of 10-billion. Light from the planets would leak around the edges.
A sophisticated instrument could even study the atmospheres of these planets, and possibly provide us with evidence of life.
We’re at an exciting time in the field of extrasolar planet research, and trust me, these clever astronomers are just getting started.
Artist's conception of the Kepler Space Telescope. Credit: NASA/JPL-Caltech
It’s unclear how the Kepler space telescope’s science operations will continue, if at all, as NASA weighs what to do with the crippled spacecraft. But the agency says not to count Kepler out yet.
What’s known for sure is NASA cannot recover the two failed reaction wheels that stopped Kepler from doing its primary science mission, which was searching for exoplanets (with a focus on Earth-sized exoplanets) in a small area in the constellation Cygnus.
“We do not believe we can recover three-wheel operation or Kepler’s original science mission,” said Paul Hertz, NASA astrophysics division director, in a telephone press conference with reporters Thursday (Aug. 15).
But the spacecraft, which is already working years past when its prime mission ceased in 2010, is still in great shape otherwise, added Charles Sobeck, Kepler’s deputy project manager.
As such, NASA is now considering other science missions, which could be anything from searching for asteroids to a technique called microlensing, which could show Jupiter-sized planets around other stars with the spacecraft’s more limited pointed ability. More information should be available in the fall on these points, once Kepler’s team reviews some white papers with science proposals.
A view of Kepler’s search area as seen from Earth. Credit: Carter Roberts / Eastbay Astronomical Society
There are limiting factors. The first is the health of the spacecraft, but it is so far listed as good (except for the two damaged reaction wheels). While radiation can degrade components over time, and a stray micrometeorid could (as a small chance) cause damage on the spacecraft, right now Kepler is able to work on something new, Sobeck said.
“We have it in a point rest state right now,” Sobeck said, referring to a state where the spacecraft uses as little fuel as possible. This will extend the fuel “budget” for years, although Sobeck was unable to say just how many years yet.
Another concern is NASA’s limited budget, which (like other government departments) has undergone sequestration and other measures as the U.S. government grapples with its debt. Kepler has an estimated $18 million budget in fiscal 2013, agency officials said, adding they would need to weigh any future science mission against those of other projects being done by the agency.
The public drama began on May 15, when NASA announced that a second of Kepler’s four reaction wheels — devices that keep the telescope pointed in the right direction — had failed.
Sizes and temperatures of Kepler discoveries compared to Earth and Jupiter
“We need three wheels in service to give us the pointing precision to enable us to find planets,” said Bill Borucki, Kepler principal investigator, during a press briefing that day. “Without three wheels, it is unclear whether we could continue to do anything on that order.”
Around the same time, Scott Hubbard — a consulting professor of aeronautics and astronautics at Stanford’s School of Engineering — wrote an online Q&A about Kepler’s recovery process. He emphasized the potential loss, although sad, is not devastating to the science.
“The science returns of the Kepler mission have been staggering and have changed our view of the universe, in that we now think there are planets just about everywhere,” he wrote.
“It will be very sad if it can’t go on any longer, but the taxpayers did get their money’s worth. Kepler has, so far, detected more than 2,700 candidate exoplanets orbiting distant stars, including many Earth-size planets that are within their star’s habitable zone, where water could exist in liquid form.” (You can read about some of Kepler’s more unusual finds here.)
In February 2013, NASA’s Kepler mission discovered a new planetary system that is home to the smallest planet yet found around a star like our sun, approximately 210 light-years away in the constellation Lyra. Credit: NASA/Ames/JPL-Caltech
NASA made several attempts to resurrect the wheels. On July 18, team members tested reaction wheel four, which spun in a counterclockwise direction but would not budge in the clockwise direction. Four days later, a test with reaction wheel two showed it moving well to the test commands in both directions.
“Over the next two weeks, engineers will review the data from these tests and consider what steps to take next,” mission manager Roger Hunter said. “Although both wheels have shown motion, the friction levels will be critical in future considerations. The details of the wheel friction are under analysis.”
Mission managers successfully spun reaction wheel 4 in both directions on July 25, an Aug. 2 update said. While warning that friction could affect the usability of the wheels in the long term, the team expressed optimism as more tests continued.
Artist’s conception of “Super-Earth” exoplanet Kepler-22b, which is about 2.4 times larger than Earth. Credit: NASA.
“With the demonstration that both wheels will still move, and the measurement of their friction levels, the functional testing of the reaction wheels is now complete,” Hunter wrote in the update, the last one to go out before Thursday’s press conference.”The next step will be a system-level performance test to see if the wheels can adequately control spacecraft pointing.”
That was expected to begin Aug. 8. You can read more technical details of the tests here. Those tests, however, showed that the friction built up beyond what the spacecraft could handle. Kepler entered safe mode, it was recovered, and it is now essentially in standby awaiting more instructions.
Meanwhile, probing the data Kepler produced thus far is still revealing new planetary candidates. The current count is now 3,548 — an increase from the approximately 2,700 quoted in May — even though Kepler was sidelined in the intervening time.
There’s also a follow-up spacecraft planned: the Transiting Exoplanet Survey Satellite, which is expected to start around 2017 or 2018. It will look for alien planets in the brightest and closest stars in the entire sky, in locations that are (in relative terms) close to Earth.
