The Young Suns Exoplanet Survey (YSES)

Most directly imaged exoplanets have been found around stars that are markedly different from our Sun. To assess the occurrence rates of wide-orbit giant planets orbiting around solar analogues, we thus launched the Young Suns Exoplanet Survey (YSES). YSES is targeting a homogeneous sample of approximately 70 young, solar-type members of the Lower Centaurus Crux subgroup of the Scorpius-Centaurus association (Sco-Cen). With the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted at the European Southern Observatory's Very Large Telescope (VLT) in the Chilean Atacama desert, we are looking for Jovian companions around these 'Young Suns'. Some highlights from the survey are presented below.

Two wide-orbit, gas-giant companions around TYC 8998-760-1

We were able to take the first direct image of a multi-planet system around a young, Sun-like star. We found the planets around a young, solar analogue that is about 17 Million year old - a baby amongst other stars and especially when compariong it to our own Sun with an age of more than 4.5 Billion years. By taking several images of the star over a couple of years, we could identify two giant companions around it. The technique used to distinguish these gravitationally bound companions from unassociated background stars is visualized in the figure to the right. When blinking two epochs of observations that are centered on the host star - which resides at the origin of the coordinate system - background stars are markedly jittering around, whilst the two companions stay more or less at the same place relative to TYC 8998-760-1. This confirms the two objects as bound companions around this 'Young Sun'. The inner planet 'b' is detected at a separation of more than 160 Astronomical Units - one Astronomical Unit is defined by the Earth-Sun distance in our Solar System - and the outer planet 'c' is at least twice as far away from its Sun. This is much farther away than the separation of any Solar System planet to our Sun. Neptune, for instance, has an average distance to the Sun of approximately 30 Astronomical Units.

Two giant Jovian companions around TYC 8998-760-1. By blinking the two images that were collected on two different nights, it is easy to distinguish background sources (jittering around) from the two co-moving companions (fixed position).

To characterize these two gas-giant planets, we took data using several filters in near infrared wavelengths (from 1 to 5 microns). As visualized in the figure to the right, both companions are significantly redder than the previously identified background stars. These multi-wavelength measurements allowed us to estimate the temperature of both planets. We found that planet 'b' is as hot as 1700 K (≈ 1400°C) and planet 'c' has a temperature of approximately 1200 K (≈ 900°C). These temperatures are rather high compared to the palnets of our Solar System. Due to their youth both planets are still hot from their formation process and they will cool down continuously. Furthermore, we derived masses for both planets. We found that the inner planet weights 14 times the mass of Jupiter and the outer planet is as heavy as six times the mass of Jupiter. Even though the planets around TYC 8998-760-1 seem to be markedly different from everything we know in our own Solar System, the discovery is an important milestone, nevertheless. Future studies of this system will allow to understand the dynamics and formation processes that were shaping this Sun-like environment, which might come along with fundamental new insights into the history of our own Solar System.

Multi-wavelength observations of the planetary system around TYC 8998-760-1.
A peculiar disk around Wray 15-788 showing (i) a bright outer ring, (ii) a fainter inner arc, and (iii) a gap inbetween.

A peculiar, self-shadowed transition disk around Wray 15-788

One of the first results from YSES was the discovery of a circum-stellar disk around Wray 15-788. An image of the disk is presented in the figure to the right. We identified three main features of the disk: (i) a bright outer ring and (ii) an inner ring-like structure that are separated by (iii) a significantly fainter gap. Most intriguing is the appearance of the disk, because only half the outer ring is visible in the image. We propose that some inner structure that is misaligned with the outer material might cast a shadow on the other side of the disk that we do not see in the image. The misalignment of this inner disk might be caused by a massive (planetary) companion that is undetected so far. Future data will facilitate testing of this thery and maybe even reveal the hypothesized planet around Wray 15-788.