We often focus on the search for Earth-like planets (whatever that means) when we talk about exoplanets: planets orbiting other stars. However, another important goal is to categorize as many planetary systems as possible, determining what kind of planets orbit what sort of stars. That catalog is gradually revealing the way planets form, and how the detailed history of each system leads to what we observe today. For example, Mercury is the smallest planet in the Solar System, but it’s far from being the smallest spherical body—and nobody expects it to be the smallest planet of any star system. Now a new observation has found an exoplanet noticeably smaller than Mercury, which will help us fill in the catalog a little more.
Now researchers may have found the smallest exoplanet yet, a world with a diameter about 80 percent of Mercury’s. This planet candidate, named Kepler-37b, orbits very close to its star: its orbital radius is about 1/4 the size of Mercury’s, so it takes only about 13 days to zip around. Thomas Barclay and collaborators also identified two other planets in the same system—labeled Kepler-37c and Kepler-37d—one of which is slightly larger than Mars, and the other which has twice Earth’s diameter. [Read more…]
The orbiting Kepler observatory has been a remarkably successful project since its inception. By watching one small patch of the sky continuously, Kepler has enabled astronomers to discover upward of 2300 possible exoplanets—planets orbiting other stars. While many of those candidates likely are not actually planets, follow-up observations have confirmed 854 exoplanets as of December 28, 2012. The American Astronomical Society meeting, happening as I type this post, is devoting about 30% of its sessions to discussing recent exoplanet discoveries. This is an astoundingly rich field of study!
However, it’s also one that is remarkably accessible. Through the citizen science program Planet Hunters, non-scientists helped discover 42 planet candidates, 15 of which may lie in their system’s habitable zone—the region at which liquid water may exist on the surface.
The Planet Hunters identified 42 exoplanet candidates, including 33 with at least three transits—the more transits we can observe, the more reliable the identification as a planet, and the better the estimates of orbital characteristics. Forty of the potential exoplanets have orbits longer than 100 days, and 9 may have orbital periods greater than 400 days, placing them farther out than most previously identified worlds. [Read more…]
How quickly things can change in science: just a few years ago, we were barely able to talk about the diversity of planetary systems. Now, we are able to distinguish between planets orbiting in tight binary systems from those in wide binaries. Additionally, exoplanets in tight binaries can orbit either both stars together (circumbinary, or Tatooine-like systems) or one of two stars, where the second might be like a Jupiter in the system. In wide binaries, the second star is so far away that it’s barely attached to the system, but a new set of simulations may show that may actually lead to greater instability than experienced by planets in tight binaries.
Nathan A. Kaib, Sean N. Raymond, and Martin Duncan ran extensive computer simulations to model exoplanets residing in wide binary systems. They found that perturbations from other stars outside the binary system had a profound effect on the shape of the system’s orbits. In some cases, planets were ejected from the system entirely or ended up in larger or highly eccentric (elongated) orbits. Based on these results, the researchers argued that some of the observed exoplanet systems with eccentric orbits may actually reside in wide binary systems where we haven’t yet detected the companion stars. [Read more, and watch the video!]
Many star systems seem to resemble our own Solar System: the planets orbit their host star in the same direction that the star spins. Admittedly, the data is still sparse: it’s not always possible to get that measurement. The brief version: you need the planet to transit or briefly eclipse its host star, and you need to be able to measure the small change in the star’s spectrum. This is most easily done when the planet is close in and relatively large—a class of exoplanets known as hot Jupiters, since they are big and close enough to experience extreme temperatures. Surprisingly, some of these hot Jupiters orbit their stars the wrong way, and this misalignment is difficult to explain within the standard theory of planet formation. However, a new model suggests that if the original star system had two stars, it would mess up the protoplanetary disk, leaving orbits askew.
In this revised model, strongly misaligned orbits are the result of another factor that influenced planet formation: a second star in the system. The gravitational influence of the companion star twisted the orbit of the exoplanet, pulling it out of alignment. And, in many cases, the star would leave little trace beyond the altered orbits: Sun-like stars often form in pairs or larger assemblies, but some of them evaporate over time. [Read more….]
Every exoplanet discovery seems to bring us closer to understanding the variety of planetary systems out there in our galaxy. The latest find is particularly exciting: an Earth-mass planet orbiting around Alpha Centauri B, one of three stars in the closest system to the Solar System. The planet isn’t very Earthlike in most respects, but it’s still an incredibly exciting discovery.
However, the discovery is still exciting for a number of reasons. First is the proximity of the star system to us: Alpha Centauri is 4.4 light years away, a tiny distance in cosmic terms. The stars Alpha Centauri A and B are some of the brightest in the sky in the Southern Hemisphere. (Sorry, fellow Northern Hemisphere-dwellers; we can’t see them from here.) We don’t have starship technology to travel there, but we could conceivably send a robotic probe that could arrive within my lifetime, and 4.4 years isn’t a terribly long time for data to travel back to Earth. No one has such a probe in the works yet, but the mere fact of discovery of a planet might encourage investment in that direction. [Read more…]