Visitors from other stars

Star chart (open source stellarium program) showing the location of comet 2I/Borisov on Dec 1st, 2019, 5:36 UTC for comparison with the corresponding image in the gallery of (C) The Open University.

This year has revealed the first two visitors coming from another stellar system far away. The giveaway signature of these visits is the very hyperbolic orbit, which means that the objects are not gravitationally bound by our sun. They must have undertaken the long journey from another star to us. Many fascinating questions arise: are these distant worlds we will never get to similar to our solar system? Which elements are formed, how much water is around?

While the first visitor 1I/’Oumuamua (I=interstellar) did not show much activity (besides a surprisingly large change in its orbital acceleration presumable caused by sublimating ices), the second one 2I/Borisov is more active and can be analyzed for its chemical composition.
I submitted a request for an image to the fine online observatory operated by The Open University on the Teide (Tenerife, Spain), and tonight the COAST 14″ telescope took a 120 seconds image of 2I/Borisov. You can find the
corresponding image in the newest image gallery of, all images there (C) The Open University. Can you spot the comet? It is the tiny elongated speck in the lower right quadrant (the image covers about 1/2 degree of the sky), or have a look at the finder chart shown here.

In addition to the hyperbolic orbit, both objects showed a non-gravitational acceleration (discussed here before for the solar-system comet 67P/Churyumov-Gerasimenko). Both interstellar comets show a rather large extra acceleration if compared to Jupiter family comets.

Non-graviational acceleration of Jupiter family comets (taken from the JPL Small-Body database), compared with the two visiting comets (preliminary orbit data from JPL).

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