Tag Archives: Kepler-22

A Thousand Planets

Depending on where you get your information from and how much weight you lend it, we have reached a thousand known planets.

Some of the semi-official sites like exoplanet.eu and more official sites like NASA’s Exoplanet Archive show less than this number. In the case of the latter because it appears they only accept planets that have made it past peer review, which is a reasonable, if not high, standard. In the case of exoplanet.eu, while it has been a valuable asset since 1995, it has missed a few planets here and there as time has gone on (especially during a recent overhaul of the site). There’s a number of other anomalies there, but it’s a site run by a guy in his spare time so there’s a limit to how much you can expect of it. That being said, it’s still a very valuable resource.

There exists a fairly small group of people, myself shamelessly included, who keep tabs on extrasolar planet news and developments nearly religiously. The count varies from person to person, but I am not alone in asserting that there are now 1,000 known planets. By my count, we’ve passed that a couple months ago, but I’ve decided to give it more time to help cover some margin for error in the planet count.

Where does this margin of error arise? There’s a number of planets whose disposition is not very clear. They have been proposed and later disputed, but not fully disproven. There are planets that are unconfirmed, but confident enough that they can be talked about as real planets. And lastly there are Kepler candidates that have been determined to be planets, but in some cases have not even been included in a preprint on arXiv yet. As such, it is not possible for me or anyone to point to a specific planet and say “this is the thousandth known planet.”

In the big picture, humanity’s first thousand planets is only the top layer of H2O molecules of the iceburg of the planet population in the Galaxy. It is severely plagued by biases in favour of short-period and/or high-mass planets due to the nature of our detection methods and completeness of our detection surveys. We have found many hot Jupiters, but we know full well that this is a minority (less than 1% of stars have a hot Jupiter). It’s clear that small planets are more prevalent, it’s just a matter of detecting them.

Recently, it was announced that the nearby M dwarf GJ 667C hosts three super-Earths in its habitable zone. Taken together with the two habitable planet candidates at Kepler-64 and single habitable planet candidates in other systems, we have about a dozen targets for a search for life. Some of these planets are better candidates than others, and I won’t encourage any undue optimism by refraining from being outright by saying that some of them appear pretty unlikely candidates – a few of them look like we’re scraping the bottom of the barrel in desperate hope (I’m looking at you, HD 40307 g, GJ 163 c, Kepler-22 b, GJ 581 d).

Still, the fact that our first thousand planets contains at least a few planets where it’s not impossible for life to exist there is encouraging, especially when considering how biased our detection methods are against them. Combined with Kepler data that tells us that habitable planets are ubiquitous in the Galaxy, I am actually quite optimistic about the odds for there being a second biosphere in the solar neighbourhood.

We have learned so much in the first thousand planets, detected at a slow rate at first, but growing to over a hundred per year. It has taken us 20 years to detect the first thousand exoplanets. I would not be surprised if the next thousand come in only five years and feature many more habitable planet candidates.

Lastly, I have been dealing with some events in my “personal life” that have kept me busy, and so I have had less time to focous on extrasolar planet science and writing about it here. This is partly why this post doesn’t have a lot of meat to it. I look forward to writing more enlightening posts in the near future.

2011 Review

Arguably the most important discovery of 2011: Earth-sized exoplanets

2011 was a banner year for extrasolar planet science with the Kepler results really beginning to come in. Among the more interesting:

    Kepler results:

  • Kepler-10: Kepler’s first rocky super-Earth, with a transiting Neptune further out.
  • Kepler-11: A system of six transiting super-Earths with anomalously low density.
  • Kepler-14: A massive hot Jupiter in a binary system.
  • Kepler-16: The first transiting circumbinary planet around an eclipsing binary star.
  • Kepler-18: A system of three planets: A super-Earth and two inflated Neptunes in a 2:1 resonance. Very similar to Kepler-9 but scaled down in masses.
  • Kepler-19: A transiting sub-Jovian planet and the first case of the discovery of a second planet through transit timing variations in the transiting planet.
  • Kepler-20: A system of five planets, two of which are ~Earth-sized.
  • Kepler-21: A transiting super-Earth around a bright (V = 8.27) star.
  • Kepler-22: A transiting “mini-Neptune” in the habitable zone, and the first transiting planet in the habitable zone of any star.
  • KOI-423: First transiting planet around a subgiant star.
  • KOI-730: A remarkable system of four planets in a 1:2:4:8 resonance.
  • KOI-55: What appears to be two remnant cores of gas giants engulfed by their parent star during its red giant phase.
    HARPS results:

  • 82 Eri: Three low mass planets only a few times the mass of Earth.
  • HD 136352: Three super-Earth/sub-Jovian planets.
  • HD 39194: Three super-Earths.
  • HD 134606: Three Neptunes.
  • HD 215152: Two lower-mass super-Earths.
  • Gliese 667 C: A second planet of a few Earth-masses in the habitable zone.
  • HD 85512: A super-Earth on the inner edge of the habitable zone.

On the orbital dynamics front, in January, it was found that the HD 37124 system, which hosts three intermediate period gas giant planets of roughly equal mass, may have a 2:1 resonance for the orbit of two of its planets. Furthermore, the planet candidate orbiting Rho Coronae Borealis, one of the first planet candidates, was proven to have a true mass far outside the planetary regime. The recovery of the planets of HR 8799 in old HST data has permitted the architecture of the system to be much more constrained.

A planet around a naked-eye giant star Alpha Arietis was reported in April. Later, in August, it was revealed that a new planetary mass object has been found orbiting a pulsar. On the subject of post-main sequence stars, a candidate planet was imaged orbiting a white dwarf. On the other side of the main sequence, a planet had been found in the late stages of formation at LkCa 15.

Gravitational microlensing provided us some constraints on the abundance of rogue giant planets as well as another cold super-Earth. It turns out that rogue giant planets may be twice as frequent as main sequence stars.

Several planets around eclipsing binaries were found this year, including planets at UZ For, HU Aqr, Kepler-16, and NY Vir.

Without a doubt, one of the most exciting stories of 2011 is the discovery that one of the first known super-Earths, the innermost planet at 55 Cancri, transits its star. This is the brightest star known to have a transiting planet, and it will prove very useful for the study of these kinds of planets. While it was initially thought that the planet was rocky and iron-rich, later observations suggest that the planet must have a significant envelope of volatiles.

In summary, 2011 has been an astounding year. The focus has shifted away from gas giant planets to sub-Jovian planets — Neptunes, mini-Neptunes and super-Earths. Below is a graph that shows this year’s total planet catch compared to previous years. One thing is clear: Not only is the galaxy full of planets, but we can look forward to seeing a huge number more in the near future.

Now for some fun, some predictions for what we might have by the end of 2012:

  • 1,000 Planets on the Extrasolar Planets Encyclopaedia
  • The discovery of a ring system around a transiting planet
  • More low-mass planets in the habitable zone from both radial velocity and transit
  • Confirmation of obvious extrasolar planet atmospheric variability (cloud rotations, etc).