Title: A Disintegrating Rocky Planet with Prominent Comet-like Tails Around a Bright Star
Authors: Marc Hon, Saul Rappaport, Avi Shporer, Andrew Vanderburg, Karen A. Collins, Cristilyn N. Watkins, Richard P. Schwarz, Khalid Barkaoui, Samuel W. Yee, Joshua N. Winn, Alex S. Polanski, Emily A. Gilbert, David R. Ciardi, Jeroen Audenaert, William Fong, Jack Haviland, Katharine Hesse, Daniel Muthukrishna, Glen Petitpas, Ellie Hadjiyska Schmelzer, Norio Narita, Akihiko Fukui, Sara Seager, George R. Ricker
First Author’s Institution: Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, USA
Status: Submitted to AAS Journals [open access]
Unfortunately, not all exoplanets live forever. Like us, they too can shuffle off the mortal coil, ultimately disintegrating into dusty plumes. Sadly, that’s the case for BD+05 4868 Ab, an exoplanet orbiting a bright K-dwarf star roughly 1015 km from Earth.
Like Icarus’s wings and the Sun, small rocky planets such as BD+05 4868 Ab can be vaporised by their host stars if they stray too close. In particular, the day-side or illuminated hemisphere of exoplanets can reach temperatures that are high enough to melt their surface, thus ejecting material into the atmosphere. Due to the weak gravitational pull of small planets, this material can over time be dispersed as dust grains that trail (and sometimes lead) the planet’s orbit around its host.
Luckily for astronomers, these comet-like tails can be detected using TESS, the Transiting Exoplanet Survey Satellite. As exoplanets pass in front of their host stars, they block out some of the light, resulting in a light curve with regular dips in brightness associated with each orbit. This is known as the transit method, and it can be used to infer exoplanet properties, such as mass, atmospheric composition, and, importantly for BD+05 4868 Ab, the presence of a leading or trailing dust tail.
Figure 2. The average transit profile of BD+05 4868 Ab (red), obtained by stacking subsequent transits (grey). Adapted from Figure 1 in the paper.
The light curve of the host star is shown in Figure 1, which gives flux as a function of time in Barycentric Julian Days (BJDs). The regular dips in brightness are a telltale sign that there is an exoplanet orbiting the star and blocking its light. By stacking the individual transits of BD+05 4868 Ab from Figure 1, the authors obtained the mean transit profile which is shown in Figure 2.
While it was clear to the authors of today’s paper that they had detected an exoplanet in the TESS data, the transit of BD+05 4868 Ab was far from typical. This was due to the short ingress and long egress that can be seen in Figure 2, as well as the variation in depth for subsequent transits in Figure 1.
To understand what could have caused these irregularities, the authors attempted to fit the average transit curve of BD+05 4868 Ab using a model that allowed for both leading and trailing dust arms. Since these arms can also block light from the host star, their presence is likely to have an effect on the shape of the transit profile.
The best-fit model is presented in Figure 3. The top panel shows that the final transit model in yellow comprises a component from the leading tail in pink and the trailing tail in blue. In the bottom panel, the best-fit model is compared to the mean transit profile from TESS in red. Due to the small differences between the predicted model values and the actual data, known as residuals, the authors concluded that both a leading and trailing arm are present in the BD+05 4868 Ab system. This makes it the fourth disintegrating planet detected to date.
To better understand the dynamics of the dust tails, the authors then simulated the release of 50000 dust grains from an exoplanet orbiting a host star. The results of this simulation are given in Figure 4, which shows the density of dust grains in the exoplanet’s orbit. Evidently, there is a small leading tail and a larger trailing tail, which together cover more than 50% of the exoplanet’s orbit. From the results of the simulation, the authors were able to infer other properties of the exoplanet and its dusty tails, such as dust grain sizes of 1–10 microns, and a mass-loss rate of 10 Earth masses per Gyr.
Sadly, such a mass-loss rate suggests that BD+05 4868 Ab will entirely disintegrate within 2 Myr, a mere blip in astronomical terms. So, like Icarus, it appears that BD+05 4868 Ab did indeed fly too close to its sun. But don’t mourn its prophesied death for too long. Astronomers will be sure to glean as much knowledge as they can before it disappears, using its dusty, comet-like tails to measure its surface composition and polarisation properties with facilities such as the James Webb Space Telescope.
Astrobite edited by William Smith
Featured image credit: NASA/JPL-Caltech
