Artist's illustration of the possible disintegrating planet in the
nearby planetary system DMPP-1. Credit: Mark A. Garlick/Haswell/
Barnes/Staab/Open University
Artist’s illustration of another DMPP-discovered planetary system,
DMPP-2.
Credit: Mark A. Garlick/Haswell/ Barnes/Staab/Open University
Among the wealth of exoplanets we’ve discovered beyond our solar system,
some are temperate, some less so. New observations have now revealed
what may be a particularly inhospitable environment: a planet literally
disintegrating as it orbits its host.
Peering Through the Shroud
With initial observations in 2015, the Dispersed Matter Planet Project
(DMPP) promised an innovative approach to hunting for exoplanets closely
orbiting their hosts. Using high-cadence, high-precision radial
velocity measurements, the project targets bright nearby stars that
shows signatures of being shrouded in hot circumstellar gas. By looking
for tiny radial-velocity wiggles in the star’s signal, the DMPP team
hopes to detect small planets that are losing mass as they orbit close
to their hot hosts.
In December 2019, DMPP announced its first discoveries: six planets
orbiting around three different target stars. Now, in a new publication
led by scientist Mark Jones (The Open University, UK), the team has
revisited the first of these systems, DMPP-1, with follow-up photometry
from the Transiting Exoplanet Survey Satellite (TESS).
Intriguingly, the radial-velocity-detected planets are not the only signals from this system.
Phase-folded TESS light curve for DMPP-1, identifying a weak transit
signal with a period of P = 3.2854 days. Credit: Jones et al. 2020
Missing the Expected, but Finding the Unexpected
DMPP-1 is a 2-billion-year-old star located just over 200 light-years
away. The radial-velocity observations of this system revealed the
gravitational tugs of four planets all orbiting with periods of less
than 19 days. The radial-velocity data suggest that this system is
probably near edge-on and contains three super-Earths and one
Neptune-like planet.
Jones and collaborators began their photometric follow-up by searching
TESS data for evidence of these four planets transiting across the host
star’s face. Interestingly, they found no sign of transits at the
predicted periods — indicating that the four radial-velocity planets are
either smaller than expected, or that the system isn’t quite edge-on
after all, so the planets don’t pass directly in front of the star.
The authors did, however, find a new signal: a weak transit
detection with a period of just ~3.3 days. This signal doesn’t match any
of the known radial-velocity planets.
The depths of the seven detected transits are highly variable, with one
even consistent with a depth of zero! This variability is common for
disintegrating planets, as the cloud of ablated material is the primary
cause of the transits. Click to enlarge. Credit: Jones et al. 2020
A Disappearing Planet?
What might this marginal detection be? Its variable transit depths,
short period, and apparent small size are all consistent with a catastrophically disintegrating exoplanet —
a close-in, small, rocky planet that is so irradiated by its host that
its rocky surface is being sublimated. As time goes on, such a planet
will eventually disintegrate into nothing.
This transit signal still needs to be confirmed with additional
follow-up photometric observations. Assuming it proves to be a true
detection, however, such a disintegrating, rocky planet orbiting a
bright nearby star would provide a veritable gold mine of information.
By exploring the transit signals from DMPP-1 with future technology
like the James Webb Space Telescope, we will be able to examine the
composition of the ablated material, potentially revealing clues as to
how hot, rocky inner planets form and evolve.
Citation
“A Possible Transit of a Disintegrating Exoplanet in the Nearby Multiplanet System DMPP-1,” Mark H. Jones et al 2020 ApJL 895 L17. doi:10.3847/2041-8213/ab8f2b
