Mercury Is No Longer The Closest World To The Sun

Astronomers in Chile used the powerful 570-megapixel Dark Energy Camera (DECam) to find an asteroid with the shortest orbital period of any known asteroid in the Solar System. They did this just ten days ago. Every 113 days, the asteroid, which is about 1 kilometer across, comes as close to the Sun as 20 million kilometers (12 million miles or 0.13 au). Asteroid 2021 PH27 has the shortest period and the shortest semi-major axis of any known asteroid in our Solar System. Only Mercury has a shorter period and a shorter semi-major axis. Since the asteroid is so close to the Sun, it feels the strongest effects of general relativity of any known object in the Solar System. Scott S. Sheppard of the Carnegie Institution of Science found the asteroid 2021 PH27 by looking at data from the Dark Energy Camera (DECam) on the Vctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. Ian Dell’antonio and Shenming Fu of Brown University took pictures of the asteroid in the evening sky on August 13, 2021, as it was getting dark. Sheppard worked with Dell’antonio and Fu while using DECam to make observations for the Local Volume Complete Cluster Survey. This survey is looking at most of the large galaxy clusters in the nearby universe. They took a break from looking at some of the biggest objects millions of light-years away to look for asteroids much closer to Earth. DECam is one of the best wide-field CCD imagers in the world. It was made for the DOE-funded Dark Energy Survey (DES), built and tested at the DOE’s Fermilab, and ran by the DOE and NSF from 2013 to 2019. At the moment, DECam is used for a wide range of science programs. The Community Science and Data Center is in charge of taking care of the DECam science archive (CSDC). The NOIRLab at NSF runs the CTIO and CSDC programs. The best time to look for asteroids that are inside Earth’s orbit, in the direction of Mercury and Venus, is at twilight, just after sunset or just before sunrise. Any stargazer will tell you that Mercury and Venus never seem to get very far from the Sun in the sky and are always easiest to see near sunrise or sunset. Asteroids that orbit close to the Sun are the same.