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.
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.
Artistic representations of the only known planets around other stars (exoplanets) with any possibility to support life as we know it. Credit: Planetary Habitability Laboratory, University of Puerto Rico, Arecibo.
The International Astronomical Union issued a statement on August 14, 2013 that they have changed their official stance on two things: 1. assigning popular names to the numerous extrasolar planets being discovered, and 2. allowing the public to be involved in that naming process.
“It is therefore in line with a long-established global tradition and experience that the IAU fully supports the involvement of the general public, whether directly or through an independent organised vote, in the naming of planetary satellites, newly discovered planets and their host stars,” the online statement said.
This new stance came as a surprise to many.
“I was surprised by the IAU statement encouraging the general public input on naming astronomical objects,” said Professor Abel Mendez, director of the Planetary Habitability Laboratory at the University of Puerto Rico, in an email to Universe Today. “This is certainly something good. …So there is now a public naming procedure that includes the IAU validation but this does not exclude any other non-IAU public naming campaigns.”
As recently as late March, 2013, the IAU’s official word on naming exoplanets was, “the IAU sees no need and has no plan to assign names to these objects at the present stage of our knowledge.”
Their rationale was since there is seemingly going to be so many exoplanets, it will be difficult to name them all.
“…the IAU greatly appreciates and wishes to acknowledge the increasing interest from the general public in being more closely involved in the discovery and understanding of our Universe. As a result in 2013 the IAU Commission 53 Extrasolar Planets and other IAU members will be consulted on the topic of having popular names for exoplanets, and the results will be made public on the IAU website.”
Artistic rendition of a sunset view from the perspective of an imagined Earth-like moon orbiting the giant planet, PH2 b. Image Credit: H. Giguere, M. Giguere/Yale University
This new decision follows a line of events earlier this year where the SETI Institute and the space company Uwingu organized their own campaigns/contests for creating popular names of objects in space instead of the rather clinical, scientific names currently assigned to planets, such as HD 41004 Ab. Both events were wildly popular with the general public, but generated discussion about how “official” the names would be. The IAU issued a statement regarding the contests saying that while they welcomed the public’s interest in being involved in recent discoveries, as far as they are concerned, the IAU has the last word. Additionally, they were against “selling” names (Uwingu charged a fee to suggest a name and to vote as a fundraiser for space research.)
“In the light of recent events, where the possibility of buying the rights to name exoplanets has been advertised, the International Astronomical Union (IAU) wishes to inform the public that such schemes have no bearing on the official naming process. The IAU… would like to strongly stress the importance of having a unified naming procedure,” said the April 12, 2013 statement issued by the IAU.
Public naming campaigns are also “sanctioned” given they follow a set of rules:
1. Prior to any public naming initiative, often a vote (hereafter “the process”), the IAU should be contacted from the start by Letter of Intent sent to the IAU General Secretary;
2. The process should be submitted in the form of a proposal to the IAU by an organization. Scientists or science communicators may be involved in the process;
3. The organization should list its legal or official representatives and its goals, and explain the reasons for initiating the process for naming a particular object or set of objects;
4. The process cannot request nor make reference to any revenues, for whatever purpose;
5. The process must guarantee a wide international participation;
6. The public names proposed (whether by individuals or in a naming campaign)should follow the naming rules and restrictions adopted for Minor Bodies of the Solar System, by the IAU and by the Minor Planet Center (see here and here
for more details.
Among other rules are that proposed names should be 16 characters or less in length, pronounceable in as many languages as possible, non-offensive in any language or culture, and that names of individuals, places or events principally known for political or military activities are unsuitable.
Also, the names must have the formal agreement of the discoverers.
The new statement also has its critics. People joked on Twitter this morning whether the name of our neighboring planet Mars, named for the god of war, will have to be changed due to the new restrictions on military nomenclature.
Astronomer Alan Stern, principal investigator of the New Horizons mission to Pluto and CEO of Uwingu said he was actually not surprised at the IAU’s new statement.
“Fundamentally it’s still about the public being subservient to IAU committees that pass on recommendations,” he said via an email response to Universe Today. “Old school. Why should the IAU be a traffic cop?”
Stern also said the new statement has several contradictions from the statement the IUA put out on April 12 of this year, such as that “these [naming]campaigns have no bearing on the official naming process — they will not lead to an officially-recognised exoplanet name, despite the price paid or the number of votes accrued.” It now would appear that contests that follow the IAU’s rules are OK.
Stern said he has received letters and emails of support from other astronomers, particularly on the “no revenue” provision, noting how astronomy publications and planetariums charge money for their magazines and sky shows.
“If they can do it, why can’t Uwingu — especially since Uwingu’s revenue is used (at least in part) to further the IAU’s own goals, namely, to advance the science of astronomy, and the public’s understanding of it, worldwide?,” Stern quoted one email he received.
Also, the April statement from the IAU said they were the single arbiter of the naming process of celestial objects, while the new August statement says, “The IAU does not consider itself as having a monopoly on the naming of celestial objects— anyone can in theory adopt names the way they choose.”
The statement goes on, “However, given the publicity and emotional investment associated with these discoveries, worldwide recognition is important and the IAU offers its unique experience for the benefit of a successful public naming process (which must remain distinct, as in the past, from the scientific designation issues).”
Since this is a public debate about the public’s involvement in providing popular names for astronomical objects, please add your thoughts in the comments.
Modeling results show where the injected gas and dust ended ups only 34 years after being injected at the disk’s surface. It was injected 9 astronomical units from the central prostar and is now in the disk’s midplane. The outer edge shown is 10 astronomical units from the central prostar. Mixing and transport are still underway and the underlying spiral arms that drive the mixing and transport can be seen. Image courtesy of Alan Boss.
When we consider samples from the solar nebula, we think about comets and meteorites. These materials come from our solar system’s beginning, but the clues they give to formation don’t always mesh neatly. Thanks to a new study done by Carnegie’s Alan Boss, we’re now able to take a look at the Sun’s formation through a set of theoretical models. This work could not only help explain some of the differences we’ve discovered, but could also point to habitable exoplanets.
At the present time, a way to look back at the solar system’s early period is to theorize about tiny pockets of crystalline particles found in comets. These particles were forged at high temperatures. An alternate method of studying solar system formation is to analyze isotopes. These variants of elements carry the exact same number of protons, but contain a different number of neutrons. Unlike the crystalline particles, we can get our hands on samples of isotopes, because they are found in meteorites. As they decay, they turn into different elements. However, the initial number of isotopes can clue researchers as to their origin and how they might have journeyed across the neophyte solar system.
“Stars are surrounded by disks of rotating gas during the early stages of their lives.” says the Carnegie team. “Observations of young stars that still have these gas disks demonstrate that Sun-like stars undergo periodic bursts, lasting about 100 years each, during which mass is transferred from the disk to the young star.”
However, the study isn’t cut and dried just yet. The study of both particles and isotopes from comets and meteorites still present a somewhat confused look at early solar system formation. It would appear there’s more to the picture than just a single path of matter from the protoplanetary disk to the parent star. The crystalline grains found in comets are heat-formed and they signal that considerable mixing and outward flow occurred from materials close to the parent star and out to the perimeter of the system itself. Certain isotopes, such as aluminum, support this theory, but others, like oxygen, defy such a neat explanation.
According to the news release, Boss’ new model shows how a period of slight gravitational instability in the gas disk surrounding a proto-Sun about to go into an outburst phase, could account for these findings. What’s more, the models also predict this could happen with a wide variety of both mass and disk sizes. It shows that instability can “cause a relatively rapid transportation of matter between the star and the gas disk, where matter is moved both inward and outward. This accounts for the presence of heat-formed crystalline particles in comets from the solar system’s outer reaches.”
So what of aluminum? According to Boss’ model, the ratios of aluminum isotopes can be explained. It would appear the original isotope was imparted during a singular event – such as an exploding star sending a shock wave both inward and outward in the protoplanetary disk. As far as oxygen goes, it can be present in different pattern because it originated from sustained chemical reactions natural to the outer solar nebula and did not just happen as a singular event.
“These results not only teach us about the formation of our own solar system, but also could aid us in the search for other stars orbited by habitable planets,” Boss said. “Understanding the mixing and transport processes that occur around Sun-like stars could give us clues about which of their surrounding planets might have conditions similar to our own.”
An artist's concept of a rocky world orbiting a red dwarf star. (Credit: NASA/D. Aguilar/Harvard-Smithsonian center for Astrophysics).
Hunters of alien life may have a new and unsuspected niche to scout out.
A recent paper submitted by Associate Professor of Astronomy at Columbia University Kristen Menou to the Astrophysical Journal suggests that tidally-locked planets in close orbits to M-class red dwarf stars may host a very unique hydrological cycle. And in some extreme cases, that cycle may cause a curious dichotomy, with ice collecting on the farside hemisphere of the world, leaving a parched sunward side. Life sprouting up in such conditions would be a challenge, experts say, but it is — enticingly — conceivable.
The possibility of life around red dwarf stars has tantalized researchers before. M-type dwarfs are only 0.075 to 0.6 times as massive as our Sun, and are much more common in the universe. The life span of these miserly stars can be measured in the trillions of years for the low end of the mass scale. For comparison, the Universe has only been around for 13.8 billion years. This is another plus in the game of giving biological life a chance to get underway. And while the habitable zone, or the “Goldilocks” region where water would remain liquid is closer in to a host star for a planet orbiting a red dwarf, it is also more extensive than what we inhabit in our own solar system.
Gliese 581- an example of a potential habitable zone around a red dwarf star contrasted with our own solar system. (Credit: ESO/Henrykus under a Wikimedia Creative Commons Attribution 3.0 Unported license).
But such a scenario isn’t without its drawbacks. Red dwarfs are turbulent stars, unleashing radiation storms that would render any nearby planets sterile for life as we know it.
But the model Professor Menou proposes paints a unique and compelling picture. While water on the permanent daytime side of a terrestrial-sized world tidally locked in orbit around an M-dwarf star would quickly evaporate, it would be transported by atmospheric convection and freeze out and accumulate on the permanent nighttime side. This ice would only slowly migrate back to the scorching daytime side and the process would continue.
Could these types of “water-locked worlds” be more common than our own?
The type of tidal locking referred to is the same as has occurred between the Earth and its Moon. The Moon keeps one face eternally turned towards the Earth, completing one revolution every 29.5 day synodic period. We also see this same phenomenon in the satellites for Jupiter and Saturn, and such behavior is most likely common in the realm of exoplanets closely orbiting their host stars.
The study used a dynamical model known as PlanetSimulator created at the University of Hamburg in Germany. The worlds modeled by the author suggest that planets with less than a quarter of the water present in the Earth’s oceans and subject to a similar insolation as Earth from its host star would eventually trap most of their water as ice on the planet’s night side.
Kepler data results suggest that planets in close orbits around M-dwarf stars may be relatively common. The author also notes that such an ice-trap on a water-deficient world orbiting an M-dwarf star would have a profound effect of the climate, dependent on the amount of volatiles available. This includes the possibility of impacts on the process of erosion, weathering, and CO2 cycling which are also crucial to life as we know it on Earth.
Thus far, there is yet to be a true “short list” of discovered exoplanets that may fit the bill. “Any planet in the habitable zone of an M-dwarf star is a potential water-trapped world, though probably not if we know the planet possesses a thick atmosphere.” Professor Menou told UniverseToday. “But as more such planets are discovered, there should be many more potential candidates.”
Hard times in harsh climes-an artist’s conception of the daytime side of a world orbiting a red dwarf star. (Credit: NASA/JPL-Caltech).
Being that red dwarf stars are relatively common, could this ice-trap scenario be widespread as well?
“In short, yes,” Professor Menou said to Universe Today. “It also depends on the frequency of planets around such stars (indications suggest it is high) and on the total amount of water at the surface of the planet, which some formation models suggest should indeed be small, which would make this scenario more likely/relevant. It could, in principle, be the norm rather than the exception, although it remains to be seen.”
Of course, life under such conditions would face the unique challenges. The daytime side of the world would be subject to the tempestuous whims of its red dwarf host sun in the form of frequent radiation storms. The cold nighttime side would offer some respite from this, but finding a reliable source of energy on the permanently shrouded night side of such as world would be difficult, perhaps relying on chemosynthesis instead of solar-powered photosynthesis.
On Earth, life situated near “black smokers” or volcanic vents deep on the ocean floor where the Sun never shines do just that. One could also perhaps imagine life that finds a niche in the twilight regions of such a world, feeding on the detritus that circulates by.
Some of the closest red dwarf stars to our own solar system include Promixa Centauri, Barnard’s Star and Luyten’s Flare Star. Barnard’s star has been the target of searches for exoplanets for over a century due to its high proper motion, which have so far turned up naught.
The closest M-dwarf star with exoplanets discovered thus far is Gliese 674, at 14.8 light years distant. The current tally of extrasolar worlds as per the Extrasolar Planet Encyclopedia stands at 919.
Searching for and identifying ice-trapped worlds may prove to be a challenge. Such planets would exhibit a contrast in albedo, or brightness from one hemisphere to the other, but we would always see the ice-covered nighttime side in darkness. Still, exoplanet-hunting scientists have been able to tease out an amazing amount of information from the data available before- perhaps we’ll soon know if such planetary oases exist far inside the “snowline” orbiting around red dwarf stars.
Read the paper on Water-Trapped Worlds at the following link.
Artist’s impression of the deep blue planet HD 189733b, based on observations from the Hubble Space Telescope. Credit: NASA/ESA.
Since its discovery in 2005, exoplanet HD 189733b has been one of the most-observed planets orbiting another star, as its size, compact orbit, and proximity to Earth has made it a relatively easy target — as extrasolar planets go. From previous studies, astronomers thought the planet may have an enticing blue-sky atmosphere. Now, further examinations with the Hubble Space Telescope have confirmed this planet really does harbor an azure blue atmosphere, very similar to Earth’s ocean blue color.
But this is no ‘pale blue dot’ ocean world. It is a huge gas giant orbiting very close to its host star. It gets blasted with X-rays from its star — tens of thousands of times stronger than the Earth receives from the Sun — and endures wild temperature swings, reaching scorching temperatures of over 1,000 degrees Celsius. Astronomers say it likely rains glass – sideways — in howling 7,000 kilometer-per-hour winds.
Nope, not a place you’d want to visit.
But the new Hubble observations of its color are the first time an exoplanet’s color has been measured and confirmed. The astronomers measured how much light was reflected off the surface of HD 189733b — a property known as albedo.
“This planet has been studied well in the past, both by ourselves and other teams,” says Frédéric Pont of the University of Exeter, UK, co-author of a new paper. “But measuring its colour is a real first — we can actually imagine what this planet would look like if we were able to look at it directly.”
HD 189733b is a Jupiter-sized extrasolar planet orbiting a yellow dwarf star that is in a binary system called HD 189733 in the constellation of Vulpecula, near the Dumbell Nebula, approximately 62 light years from Earth.
The planet’s blue atmosphere does not come from the reflection of a warm ocean, but is due to a hazy, turbulent atmosphere thought to be laced with silicate particles, which scatter blue light. Earlier observations using different methods have reported evidence for scattering of blue light on the planet, but these most recent Hubble observations give robust confirming evidence, the researchers said.
To make their measurements, the team used Hubble’s Space Telescope Imaging Spectrograph (STIS) to look at the system before, during, and after the planet passed behind its host star as it orbited. As it slipped behind its star, the light reflected from the planet was temporarily blocked from view, and the amount of light observed from the system dropped – not by much, about one part in 10,000 — but this was enough for STIS to determine the albedo.
“We saw the brightness of the whole system drop in the blue part of the spectrum when the planet passed behind its star,” explains Tom Evans of the University of Oxford, UK, first author of the paper. “From this, we can gather that the planet is blue, because the signal remained constant at the other colours we measured.”
Albedo is a measure of how much incident radiation is reflected. The greater the albedo, the greater the amount of light reflected. This value ranges from 0 to 1, with 1 being perfect reflectivity and 0 being a completely black surface. The Earth has an albedo of around 0.4.
According to the team’s paper, HD 189733b has an albedo of 0.4 ± 0.12.
The team says this determination will help in future studies of the atmospheres of other extra solar planets, as well as continuing the studies of one of the most-examined planets orbiting another star.
“It’s difficult to know exactly what causes the colour of a planet’s atmosphere, even for planets in the Solar System,” says Pont [5]. “But these new observations add another piece to the puzzle over the nature and atmosphere of HD 189733b. We are slowly painting a more complete picture of this exotic planet.”
An artist's conception of how common exoplanets are throughout the Milky Way Galaxy. Image Credit: Wikipedia
A new study suggests that the number of habitable exoplanets within the Milky Way alone may reach 60 billion.
Previous research performed by a team at Harvard University suggested that there is one Earth-sized planet in the habitable zone of each red dwarf star. But researchers at the University of Chicago and Northwestern University have now extended the habitable zone and doubled this estimate.
The research team, lead by Dr. Jun Yang considered one more variable in their calculations: cloud cover. Most exoplanets are tidally locked to their host stars – one hemisphere continually faces the star, while one continuously faces away. These tidally locked planets have a permanent dayside and a permanent nightside.
One would expect the temperature gradient between the two to be very high, as the dayside is continuously receiving stellar flux, while the nightside is always in darkness. Computer simulations that take into account cloud cover show that this is not the case.
The dayside is covered by clouds, which lead to a “stabilizing cloud feedback” on climate. It has a higher cloud albedo (more light is reflected off the clouds) and a lower greenhouse effect. The presence of clouds actually causes the dayside to be much cooler than expected.
“Tidally locked planets have low enough surface temperatures to be habitable,” explains Jang in his recently published paper. Cloud cover is so effective it even extends the habitable zone to twice the stellar flux. Planets twice as close to their host star are still cool enough to be habitable.
But these new statistics do not apply to just a few stars. Red dwarfs “represent about ¾ of the stars in the galaxy, so it applies to a huge number of planets,” Dr. Abbot, co-author on the paper, told Universe Today. It doubles the number of planets previously thought habitable throughout the entire galaxy.
Not only is the habitable zone around red dwarfs much larger, red dwarfs also live for much longer periods of time. In fact, the Universe is not old enough for any of these long-living stars to have died yet. This gives life the amount of time necessary to form. After all, it took human beings 4.5 billions years to appear on Earth.
Another study we reported on earlier also revised and extrapolated the habitable zone around red dwarf stars.
Future observations will verify this model by measuring the cloud temperatures. On the dayside, we will only be able to see the high cool clouds. A planet resembling this model will therefore look very cold on the dayside. In fact, “a planet that does show the cloud feedback will look hotter on the nightside than the dayside,” explains Abbot.
This effect will be testable with the James Webb Space Telescope. All in all, the Milky Way is likely to be teeming with life.
The nearby triple star system Gliese 667, taken on June 29, 2013. Credit and copyright: Efrain Morales, Jaicoa Observatory, Puerto Rico.
Here is a great new observation of the triple star system Gliese 667 from astrophotographer Efrain Morales of the Jaicoa Observatory in Puerto Rico. Recently, one of the stars, 667 C was found to have perhaps seven planets orbiting it! If all seven planets are confirmed, the system would consist of three habitable-zone super-Earths, two hot planets further in, and two cooler planets further out. Scientists say that the ‘f’ planet is “a prime candidate for habitability.”
Efrain also created an animation of the star system, showing the stars’ movements:
The animation was created using plates from the DSS (Digitized Sky Survey) with the final image in the animation from Efrain’s observations.
Gif animation of The animation of the triple star system Gliese 667, created using plates from the DSS (Digitized Sky Survey) with the final image in the animation from Jaicoa Observatory. Credit and copyright: Efrain Morales. Click for animation.
The system is in the constellation of Scorpius and is just barely visible to the unaided eye at magnitude 5.9 – appearing as a single point of light. The three stars orbit each other in a complicated dance. The two brightest components of this system, Gliese 667 A and Gliese 667 B, are orbiting each other at about 13 times the separation of the Earth from the Sun, while Gliese 667 C is the smallest stellar component of this system, and orbits the other two stars at about 230 AU.
Efrain used a LX200ACF 12 in. OTA, F6.3, CGE mount, ST402xm CCD, Astronomik LRGB filter set.
Thanks to Efrain Morales and the Jaicoa Observatory for providing this latest look at an extremely interesting star system!
Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.
An artist's conception of a potentially-habitable exomoon. It seems reasonable that exoplanets have exomoons, and now we're going to look for them. Credit: NASA
The latest exciting undertaking in exoplanet research is the search for exomoons. A team led by Dr. David Kipping at the Harvard-Smithsonian Center for Astrophysics has jumped at this challenge. After having theoretically proven that detecting an Earth-sized exomoon is possible, the team carried out the first detailed search for an exomoon.
Are you leaning forward on the edge of your seat awaiting the results? Well here you go: the data show no evidence of a moon. That’s simply the luck of the draw. We didn’t discover an exoplanet on our first try either. I believe that this non-detection shows that we’re on the verge of our next greatest discovery.
The reasons for searching for exomoons are abundant. “Exomoons may be frequent, habitable abodes for life and so far we know next to nothing about the underlying frequency of such objects in the cosmos,” Dr. Kipping told Universe Today. “They also play an important role in the habitability of those planets which they orbit, for example the Moon is thought to stabilize the axial tilt of the Earth and so too the climate.”
The project titled “The Hunt of Exomoons with Kepler,” more commonly known as HEK, was formed with these reasons in mind. As such, the HEK project will search for exomoons that are likely to be habitable.
The first target is Kepler-22b – the first transiting exoplanet to have been detected in the habitable zone of its host star. At 2.4 Earth radii, it is too large to be considered an Earth-analog, but it could easily have an Earth-sized moon
There are currently two methods in which we may detect exomoons.
1.) Dynamic effects – the exomoon tugs the planet, which causes deviations in the times and durations of the host planet’s transits. This is similar to the radial velocity technique for detecting exoplanets.
2.) Transit effects – the exomoon may transit the star immediately before or just after the planet does. This will cause an added dip in the observed light. See this video for a great demonstration. This is similar to the light curve technique for detecting exoplanets.
The team modeled the initial transit light curves of Kepler-22b. They then injected an Earth-sized moon into the system in order to analyze the effects. While this caused clear variations in the light curve, such variations had to be above the level of noise.
As such, they also injected noise in the light curves, which mirrors that of the Kepler data. In the end, the variations in a star’s light curve due to the presence of an exomoon are much higher than the noise. The team is able to recover the correct answer with extremely high confidence.
Here Kipping et al. presents injected moon fits. As an example, the upper left-hand figure shows an exoplanet transit, with a moon transiting as well. Here the moon transits first, causing the light to be blocked, then the planet follows, causing more of the light to be blocked. Source: Kipping et al. 2013
The real data does not show deviations like the previous figure does. This non-detection implies that there is no moon with a mass greater than 0.54 times the mass of the Earth. While there is no Earth-analog in this system, there may be a smaller undetectable moon.
I asked Dr. Kipping about our chances of success in other systems. His answer: “That depends upon nature herself!” We have no idea how regularly nature produces moons in other solar systems. “There is nothing more exciting than working on a project where the answer is wholly unknown.”
But remember: two decades ago we were unsure if nature regularly produced planets. We have since observed them in abundance. I have to believe that with 168 moons in our solar system alone, we’re likely to find them in other systems. We’re on the verge of the next greatest discovery. So stay tuned because I promise I’ll be writing about it when it happens.
