Scientists with the Kepler Telescope in space announced the discovery today of the smallest planet yet found around another star, with the catalog number Kepler 37b. The new planet is smaller than Mercury, and only about 1/3 the size of Earth. That our technology is now good enough to detect a planet this small, when it is 210 light years away, is a tribute to the engineers and scientists involved with Kepler.
The new planet, one of three orbiting the nameless star we call Kepler 37, takes only 13 days to go around its star. (Mercury, the closest planet to the Sun, takes 88 days to orbit.) So conditions on the newly found planet are scorchingly hot. In one of NASA's news stories, the authors comment that a penny, laid out in its intense starlight, would soon melt.
It was only in the last year or so that we were able to find Earth-size planets orbiting other stars, and now here we are finding much smaller worlds. You can compare the planets in the Kepler 37 system with those in our own solar system in the NASA image above.
By the way, several readers asked me to comment on the chunk of rock that exploded over the Ural Mountain region of Russia over the weekend. As best we can tell, there was no connection between this cosmic visitor and the one I previewed in my previous post. It's just a coincidence that one came close by the Earth and the other fell toward Earth in the same 24-hour period. The smaller Russian chunk exploded high up, making a spectacular fireball in the sky. It appears that only small fragments made it to the ground. The injuries that were widely reported in the media came from the shock wave that spread out from the explosion in the atmosphere. This blast wave shattered windows, just at the moment when people were attracted by the fireball's intense light to look outside.
The two visitors are vivid reminders that we live in a system that has quite a bit of "cosmic debris" among the planets. We (and the Moon, and all other objects in the solar system) are subject to being hit by some of that debris at any time. Astronomers are working hard to catalog all the larger (and most dangerous) chunks that cross the Earth's orbit around the Sun. But the smaller chunks are so hard to see and so numerous, it's not currently possible to get to know them and predict their collisions with our planet.