Astronomers Suspected There Should Be a Planet Here, and Then They Took a Picture of it

To date, astronomers have confirmed 5,272 exoplanets in 3,943 systems using a variety of detection methods. Of these, 1,834 are Neptune-like, 1,636 are gas giants (Jupiter-sized or larger), 1,602 are rocky planets several times the size and mass of Earth (Super-Earths), and 195 have been Earth-like. With so many exoplanets available for study (and next-generation instruments optimized for the task), the process is shifting from discovery to characterization. And discoveries, which are happening regularly, are providing teasers of what astronomers will likely see in the near future.

For example, two international teams of astronomers independently discovered a gas giant several times the mass of Jupiter orbiting a Sun-like star about 87.5 light-years from Earth. In a series of new papers that appeared in Astronomy & Astrophysics, the teams report the detection of a Super-Jupiter orbiting AF Leporis (AF Lep b) using a combination of astrometry and direct imaging. The images they acquired using the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE) have since become the ESO’s Picture of the Week.

The groups were led by Dino Mesa, a researcher with the Osservatorio Astronomico di Padova and the Instituto Nazionale di Astrofisica (INAF), and Robert De Rosa, an astronomer with the European Southern Observatory’s (ESO) Paranal Observatory in Chile. Using data from the European Space Agency’s (ESA) Hipparcos and Gaia satellites, the teams confirmed the presence of AF Lep b using astrometric measurements.

Similar to the Radial Velocity Method, this method consists of monitoring the motion of stars for signs of gravitational perturbance – which indicate the presence of orbiting planets. When consulting data on AF Leporis, the teams noticed a slight wobble indicative of a massive planet in orbit around it. These were followed up with observations using the SPHERE on the ESO’s Very Large Telescope (VLT) using its suite of advanced instruments.

This includes adaptive optics that correct for the blurring caused by atmospheric interference and a coronagraph that blocks out the brightness of a star so that light reflected from the atmospheres and surfaces of orbiting planets can be seen. When applied to AF Leporis, the two teams observed a gas giant roughly two to five times the mass of Jupiter. This makes AF Lep b the lightest exoplanet detected with the combined use of astrometric measurements and direct imaging.

The AF Leporis system shares similar features to our Solar System. As an F-type main-sequence star, AF Leporis is roughly the same size, masa, and temperature as the Sun (a G-type main-sequence star). In addition, the planet orbits its parent star at a distance similar to that between Saturn and the Sun, and the system has a debris belt with similar characteristics as the Kuiper Belt. However, the star and its system are quite young (~24 million years), which means that future studies could provide new insight into how the Solar System formed.

Further Reading: ESO, Astronomy & Astrophysics (Feb 14), Astronomy & Astrophysics (Feb 21)