Think on this for just a moment. Kepler-93 is 315 light years away, and we know the diameter of the star to within the width of the Earth. We know the diameter of one of its planets to within 120 kilometers. That’s a distance you could travel in a bit more than an hour on an interstate highway. Give or take.
Twenty Percent Off
Contrary to popular belief, we haven’t directly observed most of the exoplanets we’ve discovered. The planets are too small and dim to be imaged directly. With the transit method, the amount the star dims determines the size of the planet relative to the star. For example, if we see a star dim by 1%, we know that the planet blocked 1% of the star, so we know the planet is 1% that of the star. To determine the size of the star, we typically look at the background flicker of starlight, which allows us to determine its size. Now a new paper in Astrophysical Journal Letters finds that we may have been underestimating the size of some stars, thus their planets may be larger than we’ve thought.
Sahara Wind
The figure below is a temperature map of the exoplanet HD 189733b. This planet is a Jupiter-type planet that orbits very close to its parent star, orbiting about once every 53 hours. Because of its short period, and relatively close distance (about 60 light years), we’ve been able to measure its surface temperature in the infrared. The result is the map above.
1776
[av_video src=’http://youtu.be/Nw_KfDEypTY’ format=’16-9′ width=’16’ height=’9′] As of this writing there are 1,776 known exoplanets. They are distributed in 1082 planetary systems. In this video, all of the exoplanetary systems are presented to scale, in a simulated flyby. The systems are also organized by date of confirmation, so you can see how planetary discovery really took off in recent years. Exoplanet …
Life Finds a Way
Yesterday I mentioned how cutting edge research can sometimes lead to false positives. Sometimes what looks like a result turns out not to be. This is part of the reason we have peer review, and why we keep testing new results. Another way to eliminate false positives is to try to discover how your experiment could be fooled. If you are looking for a result, what else could produce a similar result? This is the goal of a new paper in the Proceedings of the National Academy of Sciences, which outlines how evidence of life on an exoplanet could be a false positive.
False Positive
Last year a paper in the Astrophysical Journal announced the discovery of two super-Earths orbiting a low metallicity Sun-like star known as HD41248. This was kind of a big deal, because it demonstrated that low metallicity stars could have rocky planets. Most of the known exoplanets are around higher metallicity stars. The two planets were discovered by observing the radial motion of the star (it motion toward or away from us) as measured by the Doppler shift of the starlight. Now a new paper in Astronomy and Astrophysics demonstrates that the planets likely don’t exist.
Altered Carbon
Yesterday I talked about the 55 Cancri system, a Sun-like star which has at least four gas giant planets, two of which orbit the star much closer than Mercury in our own system. What I didn’t talk much about is the other known planet in the system, known as 55 Cancri e. It is a super-Earth with a mass about 9 times that of Earth’s. What we find is that its density is only slightly higher than Earth’s. This means it is likely a new kind of planet.
Battle of the Planets
The 55 Cancri system is in some ways very similar to our own. The star is about the same mass and size as our Sun, and it has a Jupiter-sized planet at a distance of 5.7 AU, which is just slightly more distant than Jupiter’s 5.2 AU distance. It has three other gas planets, as well as a super-earth. One would think that the system might be similar in other ways, such as having rocky planets close to the star and gas planets more distant. But this is not the case.
Twins
NASA and JPL have announced the discovery of an Earth-sized planet orbiting in the habitable zone of its star. The planet is named Kepler-186f, and is the 5th planet from its star, Kepler 186.