SMALL TIME: An artist's representation of three small extrasolar worlds in a miniature planetary system.
Image: NASA/JPL-Caltech
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Adding to its already long roster of firsts, NASA's Kepler spacecraft has found the three smallest extrasolar planets ever detected — all of them smaller than Earth, and the most diminutive no larger than Mars. The newly discovered trio forms a miniature planetary system orbiting a cool, dim red dwarf star called KOI-961.
Because they are so close to their star, the three exoplanets are too hot to support life. But unlike most previously known exoplanets, the vast majority of which are Jupiter-scale gas giants, all three are thought to be rocky worlds like Earth and the other worlds of the inner Solar System. And because red dwarfs are the most common type of star in the Milky Way, the finding suggests that the Galaxy may be teeming with rocky planets — with at least some residing in the 'habitable region' around those stars, where the temperature would be just right for water to remain liquid and life might have got a foothold.
“We need to get a census of how many rocky planets are out there to understand how Earth formed, and how common life may be in the Milky Way,” notes Sara Seager, an astronomer at the Massachusetts Institute of Technology in Cambridge who was not part of the latest study. The discovery bodes well for fulfilling that quest, she adds.
“The suggestion — but not proof — is that rocky planets are common and diverse, and that our Solar System is not some cosmic quirk composed of weirdo worlds,” agrees study collaborator Geoffrey Marcy of the University of California, Berkeley.
The Kepler findings were presented on 11 January at the semi-annual meeting of the American Astronomical Society (AAS) in Austin, Texas, by John Johnson and Philip Muirhead of the California Institute of Technology in Pasadena. A paper describing the discovery has been accepted by the Astrophysical Journal.
Kepler hunts for planets by monitoring a field of some 150,000 stars in search of a subtle, periodic dimming — a sign that an orbiting body is passing, or transiting, in front of a star, blocking a tiny fraction of light. Most of the stars Kepler examines are similar in mass to the Sun, but some are considerably smaller — including one, a red dwarf star some 40 parsecs (130 light years) away from Earth, that was among the stars flagged as a candidate for possessing one or more planets.
Crucial downsizing
Dubbed KOI-961, for “Kepler Object of Interest”, the red dwarf came under close scrutiny by the researchers. Muirhead realized early on that the Kepler mission team, which concentrates on finding planets around Sun-like stars, had overerestimated the brightness and size of the much smaller red dwarfs, which are notoriously difficult to model. On average, the red dwarfs' diameters turned out to be only about half the values listed in Kepler's official star catalog. And for KOI-961, in particular, the diameter had to be revised downwards even further: its actual size is only about one-sixth that of the Sun.
The revised estimate for the diameter of KOI-961 was crucial to discovering the latest trio, because the size of any transiting planets found by Kepler are measured only relative to the size of their parent star. The tinier the star, the tinier the transiting planet that can be detected. An essential clue came from a fortuitous e-mail that Johnson received last September from Kevin Apps, an amateur astronomer in Horley, England. Apps, a co-author on the Astrophysical Journal paper, spends his spare time studying the data on extrasolar planets and nearby stars, and he has an encyclopaedic knowledge of their properties. He alerted the rest of the team that KOI-961 bore an uncanny resemblance in colour and temperature to a well-known dwarf called Barnard’s Star. Follow-up observations with ground-based telescopes confirmed that the two stars were virtual twins. And because the size of Barnard’s Star has been very precisely measured, thanks to its location only 1.9 parsecs (6 light years) from Earth, Johnson’s team could gauge the diameter of KOI-961 — and therefore its transiting planets — with high precision.
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Reply | Report Abuse | Link to this"And because red dwarfs are the most common type of star in the Milky Way, the finding suggests that the Galaxy may be teeming with rocky planets — with at least some residing in the 'habitable region' around those stars, where the temperature would be just right for water to remain liquid and life might have got a foothold."
I understand that binary star systems are thought to be more common than single stars, and that planets are less likely to achieve stable orbit in a binary star system. While these observations of planets orbiting dwarf stars might have been able to estimate planets' orbital period and stellar proximity, its most likely that more distant orbits would be somewhat elliptical. I'd guess that an elliptical orbit averaging more than one AU around a dwarf star would produce some extreme seasonal climate variations, perhaps even completely freezing all water in the winter and evaporating it in the summer. An exoplanetary system of a dwarf star with planets in its 'goldilocks' zone with abundant water might not provide conditions stable enough to develop complex life forms.
Also, Earth's single, relatively large moon is thought to provide rotational stability that is thought to be crucial to the development of complex life forms.
Even if we find exoplanets in the golilocks zone of Sun-like planetary systems, unless intelligent life forms transmit a signal to us, how will we ever be able to determine whether life exists there? We can't even determine whether or not life exists on some of our best candidate, neighboring planets' moons!
Frankly, I think that astronomers are investing too much of our limited resources in the discovery of planets that, while they certainly offer fertile fields of study, will never provide any really useful benefit to humanity. What fun we're having, though! Just imagine colonizing a whole bunch of new Edens! By all means - we must find every planet!
Trouble is even if we find what will essentially be seen as another earth - it may be too far away to conceivably travel to or communicate with.
Reply | Report Abuse | Link to thisSuppose we do discover such a planet and could afford to send a probe to it - the probe might not even reach its destination within our lifetime - and even when it got there, it might only find bacteria.
Is that worth spending billions of dollars on? As a tax payer, I need a stronger reason than "what if?"
Did you need a stronger reason to invade Iraq than they might have WMDs? As a tax payer and a voting member of a hypothetically democratic society it is your responsibility to educate yourself on these issues. Having a strong opinion about something you know nothing about does no one any good. Do you have any appreciation of how this research creates technology spin-offs that make their way into consumer goods? Are you so eager to give up the lead in cosmology to other nations? China and India are moving ahead in space research, they would gladly take the lead. Then again, the right wing nut jobs who whine about their tax dollars being wasted on science when instead they could be wasted on bombing developing nations into oblivion or funnelled into the pockets of the obscenely rich, have no interest in science. The good lord tells them everything they need to know which they promptly ignore when it is inconvenient. If that is the case, you are on the wrong website. I'm sure there are places for those who prefer greed over knowledge.
Reply | Report Abuse | Link to thisWe do not need to survey every inch of every new planet before Cortez lands an expedition on one and sets up a new colony. Let's hope he does not kill a Montezuma in the process.
Reply | Report Abuse | Link to thisWe might be able to create an ion drive in place of a chemical rocket. That would make an unmanned round trip rocket to a nearby star possible within my lifetime. I might see a planet where a great great grandchild might live.
Robert Schmidt, right on the money, that's the answer. Thank You!!
Reply | Report Abuse | Link to thisNot likely. Even if we could build a propulsion system which might get us up to 10% of the speed of light (doubtful with present technology), and if it were ready to launch now, it would still take at least eighty years for the round trip to the nearest star. Not taking into account acceleration and deceleration times plus time to explore the target system. Unless there were to be some sort of major, unexpected discovery of a new type propulsion, we can all only dream and take those tiny steps that may someday add up.
Reply | Report Abuse | Link to thishttp://www.tauzero.aero/
When I read that life needs ground and water to form, I always wonder, why can't other forms of life evolve on non-conventional planets? How about vaporous beings? Beings that can live in extremely high temperatures? Beings that breathe carbon dioxide?
Reply | Report Abuse | Link to thisIsn't that possible?
Why do we search for life only on Earth-like planets?
Because we know life can form on Earth-like planets. We don't know if it can form under greatly different circumstances - and although there are suggestions of possible alternative chemistries of sufficient complexity to allow evolving self-replicating entities to form, there is to my knowledge nothing even close to a good case for it, and nobody would know what to look for to discover such life.
Reply | Report Abuse | Link to thisRegarding the cost, the time griffmaster spent typing his short rant, most likely cost him more in lost wages (assuming he could have been working instead) than his tax contribution to the entire Kepler program. In other words, even without any science results, he at least has already got his money's worth. Just lucky for him, Columbus didn't think the other way around was too far, even though that was the consensus at the time. (Of course Columbus was wrong, but so was the assumption that it was just too far for anyone ever to go that way.)
I think that there could be a planet out there that can support life
Reply | Report Abuse | Link to thisThere could be a planet roughly the size of earth around a dwarf star that has the right temperature that can support life. It can also be the right temperature to have water in liquid form. If there is there there could be life even if it is a single cell organism there could be a million more rocky planets out there and we have yet to discover them all.