A comparison shows an image of a comet 46P / Virtanen from ALMA (left) and an optical photo (right). ALMA resolution is 1000 times higher than the resolution of the optical image and increases the inside of the comet diffuse coma
When comet 46P / Virtanen approached Earth on December 2, scientists using the ALMA sub-millimeter array were able to carefully study the internal areas of the coma - the gaseous envelope around the nucleus.
ALMA received a photo of the comet when it was located at a distance of 16.5 million km from Earth. With a maximum approach on December 16, it approached 11.6 million km. The comet was a real gift for amateur astronomers due to the brightness and proximity to the planet, which allowed to consider the details of the object. As it approached the Sun, its ice body heated up, releasing water vapor and other particles, forming a coma and an elongated tail.
The image of the comet from ALMA increases the nucleus, showing the natural “glow” from hydrogen cyanide molecules - a simple organic molecule that forms the etheric atmosphere around the comet. An image of hydrogen cyanide demonstrates a compact gas area and an extended, diffuse and somewhat asymmetric pattern in the inside of a coma. Due to the proximity, most of the coma was resolved. Also on December 9, astronomers reviewed more complex molecules when the comet flew at a distance of 13.6 million km from Earth.
46P / Virtanen makes a revolution around the Sun for 5.5 years, which seems a short time when compared with 75 years of motion of Halley's comet. Some bright comets have periods of hundreds and thousands of years. The comet is still observed with the naked eye.
For comparison, the photograph shows the optical view of a comet from an amateur astrophotographer. They seem similar, but ALMA covers only 5 arcseconds, which is 1000 times less than optical observation. That is, ALMA picks up the small details of the comet. These and early observations of comets confirm that they are rich in organic molecules and could populate the ancient Earth with the building blocks of life.