Comet 3I/ATLAS is an interstellar object first discovered in July. An interstellar object, literally, is a body that wanders through interstellar space between stars and happens to pass through another stellar system, such as the solar system. The discovery of an interstellar object is the third after Oumuamua (2017) and Borisov (2019).
There was even speculation in some quarters that the comet that flew in from outside the solar system might be an alien spacecraft, but the National Aeronautics and Space Administration (NASA) held a press briefing on the 19th local time and dismissed it as "completely baseless." NASA said it had been unable to respond to related rumors because of the federal government's shutdown and that the release of comet photos was also somewhat delayed.
Like an asteroid, a comet is a small object that orbits the sun along an elongated ellipse, but it differs in that it has a tail of volatile materials trailing behind it. This photo of ATLAS taken from Earth was captured on the 14th with a small telescope for minor bodies. Against the background of Virgo's stars, you can see the green coma (nucleus), which is dust and gas surrounding the nucleus, and a faint tail formed as volatile materials were heated by sunlight.
ATLAS passed perihelion, its closest approach to the sun, on the 29th of last month and is now leaving the solar system. The comet has brightened recently as it approached Earth, but a telescope is still needed to observe 3I/ATLAS from Earth. 3I/ATLAS is currently visible above the horizon in the morning sky and is expected to make its closest approach to Earth around the 19th of next month. The distance then will be 270 million km, posing no danger to Earth.