Sometimes you find amazing things when you’re looking for something completely different. That’s what happened to the newly minted Dr. Kevin Stevenson. Working on his PhD project at the University of Central Florida, he found a possible new exoplanet.
In 2010, Stevenson was part of a team of astronomers studying the Neptune-sized exoplanet GJ 436b. In orbit around the red dwarf star GJ 436 some 33 light years from Earth, it was the exoplanet’s atmosphere that surprised the scientists. It seems GJ 436b has very little methane and a lot of carbon monoxide in its atmosphere, a result that contradicted their theoretical predictions. The team following up on this unexpected result using data from NASA’s Spitzer Space Telescope, the observatory launched in 2003 that reads the universe’s story in thermal infrared light.
The data held something strange and unrelated to GJ 436b’s atmosphere: a spurious signal from the red dwarf star. They started searching through archived Spitzer data to find more similar signals. “I knew that, if these signals were periodic, the most likely source was an undiscovered planet,” Stevenson said.
The team found that the signals were indeed periodic, so decided to use their last four hours of Spitzer time to observe the predicted transit of a possible planet. What they found is a candidate named UCF-1.01.
Stevenson says there was absolutely an element of luck involved in the discovery. “Other groups have been searching for a second planet around GJ 436 since 2007, but it took the right combination of luck and technique to accomplish what we’ve done here.”
The candidate exoplanet is a very interesting one. It’s small, hot, and orbits incredibly close to its star. Preliminary measurements put its diameter at about 5,200 miles, which is about two-thirds the diameter of Earth. The period of the dip in GJ 436’s light suggests UCF-1.01 orbits about 1.75 million miles away from the star. That’s seven times the distance between the Earth and the Moon and much closer than Mercury is to the Sun. At that distance, its year lasts just 1.4 Earth days and its surface temperature is probably greater than 1,000 degrees Fahrenheit (or 600 degrees Celsius).
With an orbit that close, it’s unlikely UCF-1.01 has no atmosphere, and if it did in the past it has likely evaporated. This means that the candidate exoplanet could be a cratered, geologically dead world like Mercury. Or, such proximity could have melted the planet’s surface. It might be a molten magma world. The team can’t be sure yet.
Stevenson also found hints of a second candidate exoplanet, currently called UCF-1.02, in orbit around GJ 436. But it’s too soon to confirm either candidate. Scientists need to measure the exoplanets’ mass before the discovery can be certified, but both UCF-1.01 and UCF-1.02 are too small to measure for the moment. They are both thought to have just one-third the mass of Earth.
“Given the size of the planets and faintness of the detection, we’ll likely have to wait for [the James Webb Space Telescope] to detect light from these worlds,” said Stevenson. Not only will the JWST have a better chance of “seeing” these possible exoplanets, it will also have a spectrometer on board to allow scientists to determine their atmospheric composition. Current instruments just aren’t sensitive enough. “I expect that the next generation of instruments will be able to measure its mass in the next 5 to 10 years.”
For Stevenson, there’s a personal side to this story. “It’s very exciting as a young scientist to have already made such a contribution. I hope this discovery brings a lot of positive attention to not only myself, but the whole exoplanet community.” Having your discovery of an exoplanet as part of your PhD dissertation isn’t something too many people can boast. UCF-1.01 is an exciting development for anyone interested in the growing catalogue of exoplanets, but it’s particularly exhilarating for the young scientist who found it.