The COROT mission’s 27-cm telescope has discovered the smallest exoplanet yet, with a diameter less than twice that of Earth. COROT-Exo-7b orbits a Sun-like star and highlights the ongoing space-based investigation into rocky worlds that is drawing ever closer to an Earth-mass object. This is the kind of work COROT was designed to do, flagging planetary transits across the face of a star from an orbital perch that allows long periods of uninterrupted observation and the chance to measure the size of the planets found. ESA’s Malcolm Fridlund discusses the significance of the find:
“This discovery is a very important step on the road to understanding the formation and evolution of our planet. For the first time, we have unambiguously detected a planet that is ‘rocky’ in the same sense as our own Earth. We now have to understand this object further to put it into context, and continue our search for smaller, more Earth-like objects with COROT.”
Finding a ‘super-Earth’ is one thing when you’re using radial velocity methods that peg its mass, but quite another when a transit allows a direct measurement of its size. COROT’s success reminds us that we’re at the dawn of the era of characterizing rocky worlds around other stars, an investigation that will tell us much about how common terrestrial planets are in an exoplanet population now dominated by gas giants.
What we know about COROT-Exo-7b is that it is a hot place indeed, orbiting its star in less than a day and close enough to it to boast temperatures between 1000 and 1500°C. Our online discussion began to develop overnight, after David Blank (James Cook University, AU) passed along the link to early data showing a world with 0.035 the mass of Jupiter and a radius 0.13 as large as that planet. That points to iron, and would make COROT-Exo-7b somewhat denser than Mercury.
This ESA news release speculates that the planet’s surface is covered in molten lava, or perhaps dominated by water vapor. In any case, its internal structure should provoke much further study. The paper on the new discovery is Léger et al., “Transiting exoplanets from the CoRoT space mission VII. COROT-Exo-7b: The first super-earth with radius characterized,” to be submitted to Astronomy & Astrophysics.
Addendum: Be sure to read systemic‘s take on COROT-Exo-7b, from which this:
Everything about CoRoT-7b reemphasizes the fact that planets are wont to turn up in every corner of parameter space to which observations are sensitive. In this case, a V=11 K0V star in the direction of the galactic anti-center displays 176 individual 1.5-hour 0.3 mmag photometric dips with a strict 0.854 day periodicity. These measurements suggest a 1.7 Earth-radii planet with a 20-hour year — a world that makes 51 Peg b look like Fargo North Dakota.
In any case, it’s a remarkable detection, and will be hugely influential as soon as the mass is confirmed. The planet is orbiting at only four stellar radii — with the star filling nearly a thousand square degrees of sky…