An object that seems to be a comet from around another star is speeding through the solar system. This comet, dubbed C/2019 Q4 (Borisov), marks the second time that astronomers have seen an interstellar visitor on its way past the sun.
Ukrainian amateur astronomer Gennady Borisov spotted the comet on August 30. In the days that followed, other astronomers took enough observations of the comet to show that its orbit is not bound to the sun, a telltale sign that the object is from interstellar space, says astrophysicist Matthew Holman. He is the interim director of the International Astronomical Union’s Minor Planet Center in Cambridge, Mass., which reported C/2019 Q4’s trajectory September 11 in a public bulletin.
“There have been three or four different groups that have checked the orbit and poked at it from different directions, and everybody reaches the same conclusion,” Holman says. But he cautions that the comet is close to the sun and low on the horizon, which make it difficult to observe.
