Metals found in the atmospheres of comets surprise scientists
Metal atoms have surprisingly been discovered in the frigid atmosphere of the first known interstellar comet to visit our Solar System. Astronomers have also detected metal in the cold halos surrounding comets local to the Solar System, which suggest our Solar System comets and the interstellar visitor may have similar origins.
Scientists often deduce the composition of comets by examining the clouds of gas and dust known as comas that surround the hearts of comets. Scientists do not typically detect metals such as nickel in the comas of comets, since their surfaces are usually too cold for metal to vaporise.
Exceptions to this rule are comets passing near or plunging into the Sun, where temperatures can readily exceed the 425 degrees Celsius (800 degrees Fahrenheit) needed for nickel vapour to form. Now scientists have detected nickel atoms in the coma of the first known interstellar comet, 2I/Borisov. First discovered in 2019, its speed and trajectory revealed it was a rogue comet from interstellar space, making it the first known interstellar comet and the second known interstellar visitor after the cigar-shaped rock 1I/2017 U1, or ’Oumuamua.
The discovery was unexpected – when astronomers first saw these nickel atoms in January using the Very Large Telescope in Chile, 2I/Borisov was far from the Sun, with an estimated temperature of -93 degrees Celsius (-135 degrees Fahrenheit). It remains uncertain how comets like 2I/ Borisov can generate metal at such cold temperatures.