Pluto is emitting X-rays according to a new paper published in the journal Icarus. Scientists believe that is evidence that the former planet’s tenuous atmosphere – one few expected even existed a few years ago – is escaping into space. And while what was found is happening more than four billion miles away, that it was discovered at all is - in essence - a local story.
The Chandra X-Ray Observatory, which spotted the X-rays, is unequivocally the single best imaging X-Ray telescope ever built. And while it’s in orbit around Earth. Its real home, its center of operations, is the Chandra X Ray Center, right in our backyard.
"X-ray astronomy really lives in here. In Cambridge," said astrophysicist Scott Wolk.
"Here," specifically, is the Harvard Smithsonian Center for Astrophysics, where Wolk works as a member of the Chandra science operations team. It’s here at the center that Chandra was conceived and designed. One of its cameras was built in Porter Square – the other at MIT’s Lincoln Laboratories in Lexington.
"So really the entire spacecraft, the guts of what takes the pictures, comes from this area," said Wolk.
Big, high energy events – like super novas – produce a lot of X-rays. And Chandra was designed to peer deep into space – and back into time – to spot them.
"So X-Ray astrophysicists are very interested in the big bang, the first reionozation, the very hottest things that ever happened," said Wolk.
Chandra was launched in 1999 with a heady mandate: Find a way to calculate the distance between us and the most faraway galaxies, better understand the structure of the universe, and find the first black holes.
"And it worked, perfectly," said Wolk. "And then somebody comes a long and suggests something you never thought of."
Like, say, when scientists think they spot a few X-rays being emitted by a little comet and say, “how about we take this machine made to look at insanely hot things really far away and look at something comparatively cold and close?”
"Comets are basically room temperature," said Wolk. "They’re not a hundred million degrees, they’re not ten million degrees. So how did this happen?"
Thanks to Chandra, we now know that particles carried on the solar wind can interact with comet debris creating X-Rays – a process called charge exchange.
"And we now use these comets as distant probes of the solar wind," explained Wolk. "[They] give us extra data points, which we can begin to track how the solar wind changes as it moves away from the Earth – something we never thought we would be able to do."
And it turns out charge transfer can occur around other things too – like Saturn’s rings.
This led some to hypothesize that it could be happening around Pluto as well. Wolk says that when NASA’s New Horizons flew by Pluto chock full of instruments, it was a once in a lifetime chance to see if X-rays could be seen around Pluto, too. Despite that fact that some scientists felt there was little chance Chandra was focussed for on Pluto. When the data was combined with New Horizons’, it paid off: Evidence of an escaping atmosphere revealed by charge exchange.
"It’s easy to say [Pluto] is a rock in space, but it’s also wrong," said Wolk. "Pluto’s not a rock, Pluto’s an ecosystem. And now we know it interacts with the sun in a very particular and interesting way that we can measure. And we think that the That I think’s a big change."
Wolk points out that what they found around Pluto was just the latest discovery for Chandra that no one ever dreamed it would be making when it launched 17 years ago – from a way to measure Dark Matter to crucial details in the hunt for exoplanets.
"People have come up with 12,000 things that they’ve thought they could discover and for the most part for every observation made there are three or four papers, so if you just do it that way there have been 50,000 things discovered by this mission. Of those 50,00 only 10 were planned.
And Wolk says that really is the point. The universe doesn’t conform to our assumptions. The payoff often comes when you’re willing to be wrong and take well-informed guesses about where - and how to watch – in order to understand why.
"There’s a huge universe out there and there’s always going to more things to learn and more to understand and more to come to grips with your belief system on," said Wolk. "It may be uncomfortable. We’re not the center of the universe anymore. If the universe is that big – that’s OK. But what can I give to it? And what doe that mean about how important each individual person on Earth is?"
Big questions that they’re aiming to help answer, one X-ray photon at a time, right here in Cambridge.
