A Planet Soon to Meet Its Demise


A tiny telescope has discovered a scalding hot world orbiting its star 1,300 light-years from us. KELT-16b may only be around for a few more hundreds of thousands of years, however.

Don’t Underestimate Tiny Telescopes


The KELT-North telescope in Arizona. This tiny telescope was responsible for the discovery of KELT-16b. [Vanderbilt University]

In an era of ever larger observatories, you might think that there’s no longer a place for small-aperture ground-based telescopes. But small ground-based telescopes have been responsible for the discovery and characterization of around 250 exoplanets so far — and these are the targets that are especially useful for exoplanet science, as they are more easily followed up than the faint discoveries made by telescopes like Kepler.

The Kilogree Extremely Little Telescope (KELT) consists of two telescopes — one in Arizona and one in South Africa — that each have a 4.2-centimeter aperture. In total, KELT observes roughly 70% of the entire sky searching for planets transiting bright hosts. And it’s recently found quite an interesting one: KELT-16b. In a publication led by Thomas Oberst (Westminster College in Pennsylvania), a team of scientists presents their find.

KELT-16b light curves

Combined follow-up light curves obtained for KELT-16b from 19 transits. The best-fit period is just under a day. [Oberst et al. 2017]

A Hot World

KELT-16b is what’s known as a hot Jupiter. Using the KELT data and follow-up observations of 19 transits, Oberst and collaborators estimate KELT-16b’s radius at roughly 1.4 times that of Jupiter and its mass at 2.75 times Jupiter’s. Its equilibrium temperature is a scalding 2453 K — caused by the fact that it orbits so close to its host star that it completes each orbit in a mere 0.97 days!

This short period is extremely unusual: there are only five other known transiting exoplanets with periods shorter than a day. KELT-16b is orbiting very close to its host, making it subject to extreme irradiation and strong tidal forces.

Based on KELT-16b’s orbit, Oberst and collaborators estimate that the planet began a runaway inspiral by the age of 1 billion years. Now, at ~3.1 billion years old, KELT-16b is orbiting at a radius of just over 3 stellar radii above its host’s surface. The authors estimate that KELT-16b’s continuing inward spiral could end in the planet’s destruction by tidal forces in as little as another 550,000 years.

What We Can Learn from KELT-16b

transiting exoplanets

KELT-16b in context with other transiting-exoplanet discoveries on a diagram of planet radius vs. period. Only five other planets have been found with periods shorter than a day. [Oberst et al. 2017]

This highly irradiated world makes for an especially useful target due to its short period (which means we can observe many transits) and bright host (which means follow-up observations are more convenient and have a large signal-to-noise ratio).

In particular, with followup observations of KELT-16b from missions like Hubble, Spitzer, and eventually the James Webb Space Telescope, we can learn more about open questions in exoplanet atmospheric processes — like how heat is transferred vertically through the atmosphere, or what happens at the day-to-night terminator line on such a highly irradiated planet.

In addition, by studying KELT-16b, we can hope to gain overall insight into hot Jupiter formation and migration. The ease of observing this planet and the wealth of information it can provide will likely make it one of the top-studied exoplanets. KELT-16b has a lot to teach us before it’s torn apart!


Thomas E. Oberst et al 2017 AJ 153 97. doi:10.3847/1538-3881/153/3/97