Seven years ago, a pair of scientists scrubbing high-resolution images of space caught fleeting glimpses of a bright round object peeking from a large cloud of icy objects more than two billion miles from Earth.
As if the whole scene was not exciting enough, the object appeared to be a giant comet. Thought to be between 60 and 100 miles wide, that was it largest comet a human had ever witnessed. And it seemed to be heading towards us, very loosely speaking.
Last month, the discoverers of the giant object – astronomers at the University of Pennsylvania, Gary Bernstein and Pedro Bernardinelli – combined their previous data with recent observations of the distant object this summer and confirmed their suspicions.
Yes, it’s a mega comet. “Comet’s almost spherical cow,” they said in the title of their paper, which they submitted for publication in The Astrophysical Journal Letters on September 23rd. And the couple has also learned that the comet’s orbit will swing between Uranus and Saturn in 2031.
In addition to creating an astronomically large joke, the Bernardinelli-Bernstein comet is a very rare and unique prize for any scientist trying to put together the history of the solar system. “It’s essentially a time machine,” Amy Mainzer, an astronomer and comet expert at the University of Arizona, told The Daily Beast. The comet’s journey is a lifetime opportunity for scientists eager to learn about the conditions and building blocks of the solar system that one day led to Earth and its entire life.
A comet is a returning guest from the collisions between space rocks that created the Earth and almost everything else in our space corner a very long time ago. “The story told by the comet would tell us what existed in the solar system billions of years ago, and we can use it to understand the things we see today elsewhere in the solar system,” Bernardinelli told The Daily Beast.
But every comet we have been fortunate enough to study so far has changed much over time – either because they were too small to avoid fragmentation, or because they passed so close to the Sun that they were in the star’s intense heat and changed say their chemistry. This means that the story it tells about the early solar system has, to say the least, been edited by external forces.
Bernardinelli-Bernstein has escaped both fates. “It’s untouched,” Bernardinelli said. “Not much has happened to this object since its formation in the early days of the solar system, and therefore we can regard it as a window into the past.”
Because it is so much larger than other known comets — the famous Hale-Bopp comet, which itself is on the larger side, measures only 37 miles across — Bernardinelli-Bernstein possesses enough gravity to hold together while lazily looping through space. It’s harder to separate.
The extreme distance of the comet to the Sun also helped to preserve it. “It spends most of its time in deep-freezing the outer solar system,” Mainzer explained. Models of the megacomet’s orbit indicate that it last entered our part of the solar system about five million years ago and did not come closer than Uranus. From that distance, the heat of the Sun hardly touched it.
Mainzer says that the comet she affectionately calls “BB” as a result probably resembles the original chemical state of the nebula that formed our solar system about 4.5 billion years ago.
Its close approach in 2031 will be a monumental time to study the chemistry of the comet and reveal what our forest neck was like before there were planets lightning around. “One of the best things about this comet is that we have a while until it approaches the sun, so we have several years to study how it brightens up when the surface is exposed to the sun’s heat,” Mainzer said.
This act of heating is critical as it causes a comet to shed huge amounts of dust particles and produce the characteristic comet tail. “By watching the show as the comet creeps closer, we will be able to tell more about which chemicals, so to speak, act as the propellant in the spray can, pushing rocky particles and dust off the surface,” Mainzer explained.
What do not do coming from the surface of the megacomet is just as important as what do. Are the reactions carbon dioxide-based or nitrogen-based? Current observations suggest that Bernardinelli-Bernstein contains much of the former, but relatively little of the latter, Bernstein said.
That mix matters. Nitrogen is really common on Pluto, the small planet (or “planetoid” if you sit with the critics) that is further from the Sun than any other main planet. It is possible that Pluto still has its nitrogen because it is too far from the sun for the chemical to evaporate.
If Bernardinelli-Bernstein really has a low nitrogen content, “it might mean that this comet lived closer to the Sun than Pluto when it was young,” Bernstein said. It could make Bernardinelli-Bernstein a closer relative to our own planet than Pluto is, chemically speaking.
Mainzer stressed that the comet’s older, colder inner layers, which do not heat up easily, could be even more interesting, as they can help reveal what exactly covered the cloud of gas and dust from which our solar system was born.
In other words, we can fill in some of the big gaps in the chemical drawings in our own evolution – and get inches closer to understanding where life and the planets that support it come from.
For all its promise, there is also a disadvantage to Bernardinelli-Bernstein’s recent discovery. A decade or more can seem like a long time to study a single object in space. But considering how long it takes to conceptualize, finance, organize, and perform a new space mission, it is actually not very far at all. The only tools we can count on examining the megacom are those we already have – or are about to finish.
“Large telescopes are our best bet now,” Bernardinelli said. These include the same telescopes that astronomers have already used to inspect Bernardinelli-Bernstein plus the optics at the Vera Rubin Observatory, scheduled to open in 2023. Bernstein said it is possible NASA’s new James Webb space telescope should launched later in the year, can also spend some time pointing to the megacom.
It is very unlikely that NASA or another space agency will build a probe to capture and collect samples from Bernardinelli-Bernstein (which, ironically, is what NASA is currently doing with the asteroids around Jupiter).
But that’s not impossible, and First, Mainzer does not give up hope that some space agency can see the value in retrieving an actual icehunk from Bernardinelli-Bernstein — and doing what it takes to smash a probe. “I think BB would be a great destination for a nearby and personal visit,” she said.