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The Planetary Society Blog
By Emily Lakdawalla
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Welcome to The Planetary Society's Blog, a guide to interesting stuff going on in space science, space exploration, and space advocacy. Have any comments?
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Dec. 20, 2011 | 15:53 PST | 23:53 UTC
There's an exciting story circulating today: A large team of researchers has announced in a Nature article the discovery of not one, but two, Earth-sized planets orbiting a star named Kepler-20. Previously, the smallest-reported exoplanet was 1.42 times the diameter of Earth (and therefore 2.9 times its volume). Today's announcement is about two planets having diameters of approximately 103% and 95% of Earth's, give or take 10% -- practically the same size as Earth and Venus. But they orbit so close to their stars that it's probably hot enough to melt glass on the surface of the smaller one, so these are definitely not Earth's twins.
I was happy today to be invited to participate in a Google+ Hangout with Fraser Cain and Nancy Atkinson of Universe Today, as well as Phil Plait (the Bad Astronomer) and MSNBC space journalist Alan Boyle. I had technical difficulties but finally managed to join about 40 minutes into the show. It was fun, and I hope to do it again!
As usual, I'm far from the first to comment on this story, but I'll try to compensate by being thorough and actually reading the paper rather than just the press release. In all scientific papers you have data (observations) and lots of detailed interpretations and often a concluding paragraph of speculation. With these exoplanet detections, there is very good data on their diameters and their orbital parameters. But when it comes to actually describing what these planets are like, there is an awful long chain of interpretations from interpretations from interpretations. I thought it'd be useful for you readers if I separated the observational facts from the quite-likely-to-be-true inferences from the downstream speculations.
First: the facts.- The data are from 670 days of observations on the star Kepler-20, also known as KOI 070, KIC 6850504, and 2MASS J19104752 + 4220194. Kepler-20 is close to the same size as our Sun, but slightly less massive and slightly less luminous. It's roughly 300 parsecs (nearly 1000 light-years) away.
- Five "periodic transit-like signals" have been detected in the Kepler data.
- Three of these have been reported previously as resulting from three planets (Kepler-20b, Kepler-20c, and Kepler-20d) with diameters 191%, 307%, and 275% of Earth's, and orbital periods of 3.7 days, 10.9 days, and 77.6 days, respectively.
- The two new "transit-like signals," named Kepler-20e and Kepler-20f, recur with periods of 6.1 and 19.6 days and result in "flux decrements" (dimming of the star) of 82 and 101 parts per million, respectively.
- These flux decrements are very small. They could result from additional planets with diameters of 87% (plus or minus about 8%) and 103% (plus or minus about 10%) of Earth's, but in theory they could also result from a background eclipsing binary that falls within the same aperture as Kepler-20.
These facts are nicely summarized in a set of diagrams provided by the Kepler mission (many thanks to the Bad Astronomer for pointing these out to me):OK, now let's move on to the inferences we can be somewhat to reasonably confident about.- Nearly all of the text of the paper concerns a sophisticated analysis performed to test the hypothesis that these two signals are "false positives," resulting from background eclipsing binaries or other things that are not planets. The results of the analysis are: "the hypothesis of an Earth-size planet for Kepler-20e is 3400 times more likely than that of a false positive, and 1370 times for Kepler-20f. Both of these odds ratios are sufficiently large to validate these objects with very high confidence as Earth-size exoplanets."
- Assuming that these are planets, measurements of the star's radial velocity from the Keck telescope provide an upper limit to their masses of about 3 and about 14 times that of Earth. These numbers are large because they basically result from the non-detection of a wobble in the position of the star in Keck data. They could definitely be a lot smaller, but they can't be any larger.
- From estimates of their masses (see below), they should produce motions of the star that could possibly be detectable from Earth "in the next few years."
So we can be pretty certain that these two signals in the Kepler data do result from the presence of two planets with diameters very close to Earth. Here's an artist's concept of the sizes of these two putative planets compared to Earth and Venus. Remember that the diameters reported here are uncertain by 8-10%.Earth-sized planets of Kepler-20An artist's concept of the smallest two of five planets suspected to orbit the star Kepler-20, compared to Earth and Venus. These two planets orbit very close to their star so would be much hotter than Earth and Venus. Their diameters are about 87% and 103% that of Earth, give or take 10%. Credit: NASA / Ames / JPL |
Now it's time for the speculation, which is found only the very last paragraph of the paper and in a table summarizing the predictions of the planets' physical properties:- Because they are close to their star, Kepler-20e and Kepler-20f are probably very hot, about 1040±22 and 705±16 Kelvins, respectively.
- Assuming those temperatures are roughly correct, because of their relatively small diameter and their proximity to their star, it is very unlikely that either Kepler-20e or Kepler-20f has a gassy envelope of hydrogen and helium; that should have been blown away by the stellar wind.
- If they don't have much gas, we can assume their composition to be a mix of silicate rock and iron-rich core. That assumption yields estimates of their masses of 39% to 167% of Earth's for Kepler-20e and 66% to 304% of Earth's for Kepler-20f.
- Both Kepler-20e and Kepler-20f could have initially accreted water with its rock and iron, but only if they initially formed beyond the "snow line" in the planetary nebula and then migrated inward to their current positions. It's very likely that they did migrate inward, given their currently very close position to their star, but it's less certain where they formed in the first place, so therefore it's impossible to know whether they started out with a significant amount of water.
- if Kepler-20f did initially form far enough from its star to have accreted water, it could retain its outer envelope of water for several billion years in its current orbit. Kepler-20e, which is both smaller and closer to the star, could not; it would lose all water to "extreme-ultraviolet-driven escape" within a few hundred million years of its arrival in its current orbit.
I love the speculation part of these papers, because they serve as nutritious food for the imagination. Exoplanet science is especially delicious; there are so very many kinds of alien worlds out there, and it's fun to imagine traveling to them or to imagine what sort of life might exist on any of these crazy planets or their moons. But the speculative parts of any scientific paper are hazardous because they're usually the most fun to write about, yet are the most likely sections of a paper to turn out to be wrong. Keep that in mind when you read stories about these Earth-sized planets!
Dec. 19, 2011 | 17:57 PST | Dec. 20 01:57 UTC
If you have an iPhone, and you are into Mars rovers, I very strongly recommend that you acquire a Hasbro my3D viewer without delay. (If you don't have an iPhone, there's still 3D coolness in this post for you, so keep reading.) The my3D basically turns your phone into an electronic View-Master, making it easy to view color images in stereo without crossing your eyes. And there's a level of coolness that the View-Master doesn't have: with the 3D Pict-o-Matic app, you can pretend your my3D is a pair of Mars binoculars, so that as you rotate in your chair your view pans around Mars.
Here's what the device looks like: Hasbro my3D viewer
From the manufacturer: "Simply insert your iPhone or iPod touch into the MY3D viewer and you are ready to experience 3D entertainment in a whole new way. Tilt and turn your iPhone or iPod touch to experience interactive and immersive 3D entertainment." |
And here's an example of a color 3D image that can be viewed with the my3D viewer. When you look through the viewer, it's like you're looking through a pair of binoculars at Mars -- everything else is shut out, and you're transported there. You can also see it in crossed-eye stereo, but trust me, it's much cooler through the viewer. "Trailbreaker" rock in my3D formatOpportunity captured the images for this view of a target called "Trailbreaker" on sol 2702 (September 1, 2011). This is a stereo pair that can be viewed as a cross-eye stereo image or using the my3D viewer for the iPhone. Credit: NASA / JPL / Cornell / color composite by Mike Howard |
It's not too late to pick up a my3D viewer for the space fan/iPhone or iTouch user in your life. (Especially if the main space fan and iPhone user in your life is you!) Unfortunately, it does seem that this is a hot item. Its list price is around $25 but it's now available online only through scalpers at double the price; you might have better luck finding it in retail stores.
I have zipped up two collections of space images suitable for my3D viewing. But you don't have to have a my3D viewer to enjoy the stereo images -- you can view them in cross-eye stereo on your own, or use any of a number of pieces of free stereo image viewing software (I like StereoPhotoMaker) to help you turn them into red-blue anaglyphs.If any of you out there owns a my3D, I would love to hear from you -- I'm not sure how popular they are and whether it'll be worth my time to post stereo image collections for them from time to time. And if you create your own collection of 3D space images, I would be delighted if you would share them with me!
I didn't buy the my3D just for space images. For personal photography I use a FujiFilm FinePix 3D camera, so now I get to review my children's growth in 3D as well. Which is awesome. Here's a photo from a trip to Washington, DC in the summer of 2010.Anahita and Viking in the National Air and Space MuseumTaken in June 2010, shortly before Anahita's fourth birthday. |
Dec. 17, 2011 | 15:31 PST | 23:31 UTC
By Charlene Anderson
Last night, the U.S. Senate voted down the House of Representatives bill that would have sliced an additional 1.83 percent from discretionary spending accounts � which includes NASA and NOAA.
The Senate did approve spending $8.1 billion in disaster relief, while rejecting the House measure that would have offset it with money taken from the discretionary accounts.
NASA's fiscal year 2012 budget will remain at $17.8 billion, still some $650 million less than the year before. NOAA remains at $4.9 billion for the year.
The fiscal year 2013 budget request from the Administration will be rolled out next February 6. It's likely that this budget will reflect the constricted fiscal environment � and there will be more cuts to space endeavors.
Stay tuned�.
Dec. 16, 2011 | 16:18 PST | Dec. 17 00:18 UTC
By Charlene Anderson
This year, the United States suffered 12 billion-dollar disasters caused by "extreme weather events" � tornadoes, hurricanes, floods, heat waves, droughts. More than 1,000 people died in these disasters.
To help the victims recover, the U.S. House of Representatives has passed appropriations bills that will provide $8.1 billion disaster aid. The Senate will vote on the measures today. If they are passed, they will go to the President for signature. There is great pressure to get this process completed because, at day's end, the previous stopgap bill to fund the U.S. government will expire. If no appropriations bill is produced and signed, a government shutdown is possible.
The political posturing and brinkmanship go on. And among the hundreds of government programs getting squeezed are those that would help us understand, predict, avoid, mitigate, and maybe even prevent future weather disasters.
To provide the $8.1 billion in relief, the appropriations bill will order a "1.83% across-the-board cut to all FY 2012 base discretionary spending, except the Department of Defense, Military Construction, and Veterans Affairs."
Among those to be cut are two government agencies that monitor Earth from space. NASA and NOAA will see their budgets drop again. NASA's will fall from $17.8 billion to $17.4 billion; NOAA's will drop from $4.9 billion to $4.8 billion.
So agencies that try to understand and address the causes of weather disasters are being cut to provide money to deal with the aftermaths of weather disasters. Yes, we must pay for the damage already done. Across-the-board cuts are an easy way to do it and do it quickly. But Congress is taking money from work that could ease future disasters. There's something twisted in this logic. But that's how governments operate.
Jane Lubchenco, NOAA Administrator, said last week, "Understanding, predicting, and managing extreme events requires an extraordinary amount of information about the physical state of the earth system, and how it's changing from moment to moment and decade to decade."
We need that information to understand the planet we live on. NASA and NOAA, and the USGS that operates the Landsat program, help provide what we need.
The arm-wrestling over the federal budget for fiscal year 2012 is almost over. The Administration will release its proposed budget for fiscal year 2013 next February 6. We have only a few weeks to gather our strength before the struggle begins again. And considering this economic and political climate, you can be sure that the battle over next year's budget will be even more difficult and divisive.
Still, we've got to get ready.
Just my rant for the day. If you want to enjoy more rants, follow me on Twitter @PlanetCharlene.
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