Astronomers Find Planet Barely Larger Than Earth's Moon

The Bad Astronomer writes "A team of astronomers has announced the discovery of the smallest exoplanet orbiting a Sun-like star yet found: Kepler-37b, which has a diameter of only 3865 kilometers — smaller than Mercury, and only a little bigger than our own Moon. It was found using the transit method; as it orbits its star, it periodically blocks a bit of the starlight, revealing its presence (abstract). Interestingly, the planet has been known for some time, but only new advances in asteroseismology (studying oscillations in the star itself) have allowed the star's size to be accurately found, which in turn yielded a far better determination of the planet's diminutive size. Also, the asteroseismology research was not funded by NASA, but instead crowd funded by a non-profit, which raised money by letting people adopt Kepler target stars."

Comments

A planet or a dwarf planet?

[maxwell demon]

A planet or a dwarf planet?

I mean, if Pluto is not allowed to be a planet, then why should such a small object be labelled as one?

Re:A planet or a dwarf planet?

[medcalf]

Not really. "Cleared its orbit" doesn't mean no co-orbital objects. All planets have LaGrange point co-orbitals for example. Pluto is different in that it has a lot of co-orbitals, and some of them are almost as large as Pluto itself. Essentially, it's a KBO rather than a planet proper, by the current definition.

Re:A planet or a dwarf planet?

[mrtommyb]

Hi, I wrote this paper: We actually looked very carefully whether this planet has cleared its neighborhood. The smallest reasonable mass we can assume for this planet is 0.01 Earth masses. With this mass it would clear its orbit of other bodies. However, if it were much further away from its star (like at the distance Pluto is from the Sun) then it would probably be considered a dwarf planet.

Re:A planet or a dwarf planet?

[Chris Burke]

Pluto is different in that it has a lot of co-orbitals, and some of them are almost as large as Pluto itself.

To make it clear how big a difference it is, let's look at the ratio of the mass of the body in question to the mass of the rest of the objects in its orbit (discounting direct satellites).

Of the planets Neptune happens to have the lowest such ratio. It outmasses everything else in its orbit by a factor of over 10,000.

Meanwhile Pluto is outmassed by the other objects in its orbit by more than a factor of ten. It is less than 10% of the mass in its orbit.

That's a five order of magnitude difference. "Clearing the orbit" isn't precisely defined... and it doesn't need to be. You don't need a precise definition of where exactly on the beach the ocean begins to know that Asia and North America are separated by the Pacific Ocean.

And I suspect that such a large distinction isn't a cosmic accident, and that other star systems of sufficient age will show a similar trend. Unfortunately it's going to be a long time before we can test this hypothesis.

Re:A planet or a dwarf planet?

[osu-neko]

I mean, if Pluto is not allowed to be a planet, then why should such a small object be labelled as one?

Shhh ... people might hear you and think you're making sense.

We can't have that.

One would hope not. It's annoying when ignorant drivel is modded "insightful" here. Just because "people hear you and think you're making sense" doesn't mean you actually are...

I have respect for people who think Pluto should still be considered a planet... assuming they also think Eris should be a planet, and long before Pluto was demoted, were upset about the fact that Ceres is not considered a planet. It's the knuckle-dragging morons who are upset about Pluto but never were bothered by Ceres not being a planet that need to get a freakin' clue. If you had no problem with Ceres not being considered a planet, you shouldn't have any problem with the fact that Pluto isn't, either.

Re:NASA

[Mindcontrolled]

Yup. If only NASA were gone, the crowd funders would have discovered the planet using data from their own frigging telescope, instead of NASA's Kepler. And call me when the "asteroid miners" produce anything but vaporware. Meanwhile, NASA is doing meaningful science.