Astronomers are scrambling to study an alien visitor from the depths of intergalactic space: the newly discovered comet called 2I/Borisov. Named after amateur Crimean astronomer Gennady Borisov, who discovered it last August, 2I/Borisov is now the cynosure of all telescopes as it hurtles across the heavens towards the Sun.
Scientists are uncertain about its origins. Some believe that a million years ago, 2I/Borisov, travelling from an unknown galaxy, approached a binary star system called Kruger 60 about 13 lightyears away from Earth. Before the star system’s gravity pulled it in, the interstellar intruder zoomed away at speeds exceeding 93,000 km/hr, its trajectory pointing it towards our Solar System. But others argue that Kruger 60 is its home.
2I/Borisov crossed the orbits of Saturn and Jupiter earlier this year and will reach its nearest point to the Sun at less than 305 million kms (about twice the average Earth-Sun distance) in late December. Some of its surface material – consisting of gas and dust – has started to peel off to form a short cometary ‘tail’. This is typical of all comets, which are essentially ice-covered blocks of gas and dust and swing through our Solar System in eccentric orbits. On approaching the Sun, a part of a comet’s surface material evaporates, making a ‘tail’ that trails the comet like streamers. When Earth passes through this cometary rubble, meteor showers or ‘shooting stars’ light up the eastern sky.
Most comets come from the Oort Cloud: a vast collection of rocky, icy bodies far beyond the edge of the Solar System. Occasionally, a neighbouring star’s gravitational tug loosens one of these comets and sends it careening Sunwards, or outward into interstellar space where it drifts until it is captured by the gravity of another star. Wanderers from deep space like 2I/Borisov, though, are quite uncommon in the Solar System and offer scientists an excellent opportunity to find out its constituents and compare it with comets of the Oort Cloud.
In fact, this is only the second time astronomers have been able to study an interstellar nomad in detail. In 2017, a cigar-shaped object called ‘Oumuamua quickened the pulse of the scientific community when it zoomed past Earth. One scientist even speculated on the possibility of it being a spaceship. But the mysterious object left the Solar System without yielding any definitive clues about its origins.
Comets and asteroids are remnants from the early Solar System. By studying them up-close, astronomers hope to better understand how planets and their moons formed. “Interstellar objects like 2I/Borisov offer a unique lens into the processes occurring in extrasolar systems,” Malena Rice of Yale University told this author in an email. “Generally, these systems need to be studied at vast distances that make it difficult to discern details. But objects like Borisov provide a completely new way to study material from extrasolar systems up close. They can help us to better understand what planetary systems other than ours are made of and how they form and evolve.”
What is remarkable about 2I/Borisov is that its high velocity of 35 km/s – the average velocity of nearby stars relative to the Sun is approximately 20 km/s – and hyperbolic orbit rule out its origin in the Oort Cloud. At the same time, many of its characteristics indicate that it is no different from comets of the Solar System. A team of astronomers led by Alan Fitzsimmons of Queen’s University Belfast, for instance, has discovered cyanogen, a toxic gas, in 2I/Borisov’s coma. Composed of carbon and nitrogen atoms, cyanogen is usually found in comets of the Solar System.
Its presence in an interstellar comet suggests that it is commonplace in most, if not all, cometary bodies across the universe – and that the same chemical processes take place on comets everywhere. Methane, for example, has been found in abundance on many comets while on Earth, bacteria routinely produce methane from carbon dioxide.
Does this then reinforce the theory that comets first brought organic molecules – the building blocks of life – to Earth four billion years ago? Although these molecules could not have endured the incinerating temperatures on the infant Earth, if they were delivered in a frozen state by comets, it is not implausible that they bequeathed the legacy of organic life to this planet. Maybe it is no coincidence that microbial life started on Earth at a time when the Solar System was bombarded by innumerably more comets than it is now.
With astronomers building ever more sophisticated telescopes, they are likely to discover an increasing number of visitors from faraway stellar systems. “Planets of roughly Neptune’s size may be common in new-born planetary systems,” Rice says. “These are exactly the type of planets that can efficiently transfer energy to Borisov-like comets to eject them from the (star) system. With the upcoming Large Survey Synoptic Telescope, we should be seeing more interstellar comets in the near future – a few large objects a year and up to a hundred smaller ones per year.”
For all we know, it is possible that one of them turns out to be the message in a bottle that tells us where we came from.