Free Astronomy Magazine November-December 2019

20 NOVEMBER-DECEMBER 2019 SPACE CHRONICLES ous invaluable insights. For example, it offers clues to the chemical com- position, structure, and dust char- acteristics of a planetary building block presumably forged in an alien star system a long time ago and far away. “Because another star system could be quite different from our own, the comet could have experi- enced significant changes during its long interstellar journey. Yet its properties are very similar to those of the Solar System’s building blocks, and this is very remarkable,” said Amaya Moro-Martin of the Space Telescope Sci- ence Institute in Balti- more, Maryland. Hubble photographed the comet at a distance of approximately 420 mil- lion kilometres from Earth. The comet is travel- ling toward the Sun and will make its closest ap- proach to the Sun on 7 December, when it will be twice as far from the Sun as Earth. It is also follow- ing a hyperbolic path around the Sun, and is currently blazing along at the extraordinary velocity of over 150,000 kilome- tres per hour. By the mid- dle of 2020, the comet will be on its way back into interstellar space where it will drift for mil- lions of years before maybe one day approach- ing another star system. Crimean amateur as- tronomer Gennady Bori- sov first discovered the comet on 30 August 2019. After a week of obser- vations by amateur and professional astronomers all over the world, the Hubble observes first confirmed interstellar comet O n 12 October 2019, the NASA/ESA Hubble Space Telescope provided astronomers with their best look yet at an interstellar vis- itor — Comet 2I/Borisov — which is believed to have ar- rived here from another plan- etary system elsewhere in our galaxy. This observation is the sharpest view ever of the in- terstellar comet. Hubble re- veals a central concentration of dust around the solid icy nucleus. Comet 2I/Borisov is only the second such interstellar ob- ject known to have passed through our Solar System. In 2017, the first identified in- terstellar visitor, an object dubbed ‘Oumuamua, swung within 38 million kilometres of the Sun before racing out of the Solar System. “Whereas ‘Oumuamua looked like a bare rock, Borisov is really active, more like a normal comet. It’s a puzzle why these two are so different,” explained David Jewitt of UCLA, leader of the Hubble team who observed the comet. As the second interstellar object found to enter our Solar System, the comet provides vari- by NASA/ESA O n 12 October 2019, the NASA/ESA Hubble Space Tele- scope observed Comet 2I/Borisov at a distance of ap- proximately 420 million kilometres from Earth. The comet is believed to have arrived here from another planetary sys- tem elsewhere in our galaxy. [NASA, ESA, D. Jewitt (UCLA)]