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【TDLI】One Step Closer to the Discovery of a Second Solar System

August 13, 2021      Author:

Before Nicolaus Copernicus proposed the Heliocentrism in the 16th century, the Earth was thought to be the center of the universe. Because our ancestors observed the universe from a terrestrial perspective, the stars, the Moon, and the Sun apparently move around the Earth. After the observational evidence supporting the Heliocentrism found by Galileo Galilei and Johannes Kepler, people began to realize that the Sun is probably the center of the universe. Until the discovery of extragalactic worlds by Edwin Hubble in 1920s, people started to believe that neither the Sun nor the Milky Way is the center and there is probably no center of the universe. However, as the only habitable place of human beings, the Earth in the Solar System has a central role in the origin of life and human being. After the discovery of the first exoplanet in 1995, astronomers began to find planets similar to the Earth (or second Earth) and planetary systems similar to the Solar System (or second Solar System) to test whether the Earth in the Solar System is the only place to host life.

Figure 1. Diagram of the solar system

Although the current technology is still a little far away from the discovery of the second Earth, it is mature enough to detect the analogs of Jupiter, Saturn, Uranus, and Neptune (we call these giant planets “Jupiter analogs”), and is thus sensitive to Solar System analogs. The radial velocity method (measuring the Doppler shift of a star caused by a planet) has been used to find Jupiter analogs, but it can only give the minimum mass. Compared with the radial velocity method, the astrometry method (measure the positional wobble of a star caused by a planet) is able to give 2D information of the stellar motion. Hence it can constrain the absolute mass and all orbital elements of Jupiter analogs. Being launched in 2016, the European Space Agency’s Gaia satellite is able to measure the positions of stars to tens of microarcsecond (~2.8x10^-8 rad) precision, and will probably find about 10,000 Jupiter analogs eventually.

Figure 2. Diagram of the Solar System analog

Recently, Tsung-Dao Lee Fellow Fabo Feng, as the leader of an international group, has discovered the smallest Jupiter analog with a mass of about 2 Jupiter mass based on an innovative use of the data from Gaia and its precursor Hipparcos launched 24 years before. The cooling model of Jupiter analogs predict a temperature of 123-176K for GJ 777 b, similar to the Jupiter’s temperature of 134K. This makes GJ 777 b the most robust Jupiter analog.  Furthermore, GJ 777b is separated from its host by 0.25’’, and making it suitable for direct imaging by future space telescopes such as the James Webb Space Telescope (JWST) and the Roman Space Telescope (RST) for the study of planetary atmosphere and bulk composition.

The lead author Prof. Feng said excitedly, “when the Gaia data was released, many groups tried to use the high precision astrometry data from Gaia to find exoplanets. Compared with the other groups, our group thoroughly analyze the positional and proper motion difference between Gaia and Hipparcos, and detect an astrometric signal as small as 0.2 mas from GJ 777 b. This opens a new window for the discovery of a large sample of Jupiter analogs. ”

In this work, the Hipparcos-Gaia astrometry difference as well as radial velocity data have also been used to detect and strongly constrain the orbits and masses of seven brown and red dwarfs. The radial velocity data were obtained by the APF high precision spectrograph in the Lick Observatory and the HIRES spectrograph installed on one of the 10-m Keck telescopes. The other radial velocity and astrometry data are available to the public. Through the efforts from Prof. Feng and Profs. Paul Butler and Alan Boss in the Carnegie Institute for Science, Profs. Steven Vogt and Bradford Holden in the Lick Observatory, Dr. Jenniffer Burt in the NASA JPL, Prof. Rebecca Oppenheimer in the American Museum of Natural History, Prof. Hugh Jones in the University of Hertfordshire, and Dr. Mark Phillips in the University of Exeter, this work was published in the Monthly Notices of the Royal Astronomical Society on 3 August 2021( ), and will have a high impact on the discovery of Solar System analogs through combined analyses of astrometry and radial velocity data.



Source: Tsung-Dao Lee Institute, SJTU