Several scientific organizations have announced the detection of what appears to be an interstellar comet, which has consequently received the designation 3I/ATLAS. It could be a large comet, with an estimated width of around 20 kilometers, but the first estimates of the size of its nucleus are still very rough. Its trajectory will take it within the orbit of Mars, but, together with its considerable speed, it will only lead to a limited direction change by the Sun’s gravity. Unfortunately, it will never get close enough to Earth to allow detailed observations, but any interstellar object is very interesting for astronomers. This is the third officially recognized “visitor” after 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019.

An article published in “The Astrophysical Journal Letters” reports a study on comet C/2014 UN271 (Bernardinelli-Bernstein) conducted thanks to observations made with the Hubble Space Telescope. A team of researchers also used previous observations to estimate that this comet’s nucleus is about 119 kilometers in diameter. This result confirms that it’s the largest known comet. The studies will continue even if it will remain very far from Earth also because it almost certainly comes from the Oort cloud.

An article published in the “Astronomical Journal” reports the results of a study on comet C/2019 Y4 (ATLAS) whose conclusion is that it’s a fragment of a larger comet whose passage could have been seen on Earth about 5,000 years ago. A team of researchers led by astronomer Quanzhi Ye of the University of Maryland in College Park used observations conducted with the Hubble Space Telescope to examine this comet and its orbit. In fact, there are now various fragments and it’s possible that the progenitor gave rise to an entire family of comets. Amateur astronomer Maik Meyer identified a correlation with C/1844 Y1, nicknamed the Great Comet of 1844.