Collaborative Research: EXPRES Search for Low Mass Planets

Lowell Observatory, Flagstaff AZ

Investigators

Abstract

A collaborative team from Yale University, Lowell Observatory, and San Francisco State University will conduct a survey for small, temperate planets orbiting nearby stars. Virtually every star forms with planets. However, none of the planets so far detected are like the Earth. Many are gas giants, similar to Jupiter or Neptune. The only small rocky planets that have been detected orbit very close to their host stars, where inhospitable temperatures reach thousands of degrees. The discovery of other worlds that are similar to the Earth could help astronomers to find life on other planets. Unfortunately, the tiny signals from Earth-like planets are difficult to detect. This investigation will employ a new detector with the precision needed to detect potentially habitable worlds. The investigation will carry out a survey of bright, nearby stars with the goal of detecting planets that are similar to the Earth. This program places undergraduates and masters students from an officially recognized minority serving institution, with almost 41% of students having Chicano/Mexican or Latino background, at the forefront of exoplanet research. SFSU students will be collaborating with their peers at Yale and Lowell Observatory in observing, improving RV and planet atmosphere analysis tools, and improving understanding of planet formation. Students will also be learning to communicate these results with the Spanish speaking public and developing materials that can be shared outside of their community. The primary aim of this project is to detect low mass planets in both compact and Solar System like architectures. These planets have been missed by previous radial velocity surveys. This will allow the reconciliation of different planet populations seen by transit and radial velocity surveys and to better understand planet formation and evolution. The EXPRES spectrograph is calibrated with a stable laser frequency comb and has sufficient precision to find analogs of the small radius planets seen by Kepler transits. Following a carefully vetted set of 50 stars at high cadence over the next three years will allow the project find planets missed by transit surveys: these are small planets with orbital periods longer than 100 days. In addition, flexible scheduling of nearly 200 partial nights per year coupled with a remarkably stable instrumental profile enable Rossiter-McLaughlin measurements to determine orbital obliquity and detection of planet atmosphere constituents with high dispersion spectroscopy. The observational limitations of prior RV surveys and the unfavorable probability for detection of long period transits have left the occurrence rate of low-mass planets with periods longer than 10 days poorly constrained. At first glance the exoplanet populations appear to disagree for RV and transit surveys. The leap in radial velocity precision opens up an entirely new parameter space, allowing for detection of low mass planets in orbits longer than 40 days. It is likely that there are no other ways to detect these planets - this parameter space will be unexplored by current transit surveys. The investigation will reach the parameter space where Earth-like planets at habitable zone distances orbit around G and K stars. The highly stable measurements will also enable planet atmosphere studies and provide new insights into the behavior of stellar photospheres. The proposed survey will advance understanding of rocky planet occurrence rates and detect Earth-like planets in habitable orbits around Sun-like stars. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.