Space instrumentation

Abstract:

We have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (~1.5-2.5 M_sun) conducted to date and includes the planet hosts beta Pic and Fomalhaut. We obtained follow-up astrometry of all candidate companions within 400 AU projected separation for stars in uncrowded fields and identified new low-mass companions to HD 1160 and HIP 79797. We have found that the previously known young brown dwarf companion to HIP 79797 is itself a tight (3 AU) binary, composed of brown dwarfs with masses 58 (+21, -20) M_Jup and 55 (+20, -19) M_Jup, making this system one of the rare substellar binaries in orbit around a star. Considering the contrast limits of our NICI data and the fact that we did not detect any planets, we use high-fidelity Monte Carlo simulations to show that fewer than 20% of 2 M_sun stars can have giant planets greater than 4 M_Jup between 59 and 460 AU at 95% confidence, and fewer than 10% of these stars can have a planet more massive than 10 M_Jup between 38 and 650 AU. Overall, we find that large-separation giant planets are not common around B and A stars: fewer than 10% of B and A stars can have an analog to the HR 8799 b (7 M_Jup, 68 AU) planet at 95% confidence. We also describe a new Bayesian technique for determining the ages of field B and A stars from photometry and theoretical isochrones. Our method produces more plausible ages for high-mass stars than previous age-dating techniques, which tend to underestimate stellar ages and their uncertainties.

Abstract:

Why are the terrestrial planets so different? Venus should be the most Earth-like of all our planetary neighbours. Its size, bulk composition and distance from the Sun are very similar to those of the Earth. Its original atmosphere was probably similar to that of early Earth, with large atmospheric abundances of carbon dioxide and water - possibly even a liquid water ocean. While on Earth a moderate climate ensued, Venus experienced runaway greenhouse warming, which led to its current hostile climate. How and why did it all go wrong for Venus? What lessons can we learn about the life story of terrestrial planets in general, whether in our solar system or in others? ESA's Venus Express mission proved very successful, answering many questions about Earth's sibling planet and establishing European leadership in Venus research. However, further understanding of Venus and its history requires several more lines of investigation. Entry into the atmosphere is required to measure noble gas isotopes to constrain formation & evolution models. Radar mapping at metre-scale spatial resolution, and surface height change detection at centimetre scale, would enable detection of current volcanic & tectonic activity. A lander in the ancient tessera highlands would provide clues as to the earliest geologic record available on Venus. To address these themes we propose a combination of an in situ balloon platform, a radar-equipped orbiter, and (optionally) a descent probe. These mission elements are modelled on the 2010 EVE M3 mission proposal, on the 2010 EnVision M3 proposal, and on Russia's Venera-D entry probe, respectively. Together, these investigations address themes of comparative planetology and solar system evolution. This document was submitted in May 2013 as a response to ESA's Call for White Papers for the Definition of Science Themes for L2/L3 Missions in the ESA Science Programme.