Depending on how you look at it, UC Irvine doctoral candidate Te Han and his adviser, Paul Robertson, just made an already unimaginably difficult job – finding and observing planets outside our solar system – a lot harder or a lot more accurate.
Either way, what both men insist they didn’t do is transmogrify into the bane of exoplanet researchers everywhere – “planet killers” – people whose work dents or even erases work that might bring humanity closer to hooking up with other intelligent life forms.
“This isn’t a flaw that we just discovered,” Han said. “It’s something people were already worried about. We just (brought) out the details of it.”
The “it” Han is talking about is light. Specifically, he’s referencing solar light that’s essential to finding and observing exoplanets (planets that reside outside our solar system), and that sometimes – when issued by more than one star – can prompt a miscalculation of a planet’s size and composition.
Even more specifically, Han is talking about solar light viewed through NASA’s Transiting Exoplanet Survey Satellite, or TESS, which launched seven years ago and has become the space telescope of choice in the fast-growing world of exoplanet research. To date, researchers have used TESS to confirm the existence of 638 exoplanets, or slightly more than 10% of all the exoplanets currently known to exist, and to find another 7,655 celestial bodies that are still subject to research that might confirm or disprove their status as exoplanets.
In exoplanet research – which is key in the search for intelligent life – light is a huge deal.
Exoplanets are discovered only after they pass in front of the light generated by the star that serves as their version of the sun. By blocking light, an exoplanet’s shadow can reveal its size and composition and, by inference, its potential to host intelligent life.
That’s been the theory, anyway.
According to a paper with the on-the-nose title “Hundreds of TESS Exoplanets Might Be Larger than We Thought,” written by Han and Robertson and others, and published this week in Astrophysical Journal Letters, light contamination (light generated by more than one or more nearby star) might be skewing a lot of what planet hunters have been finding via TESS technology.
In all, about 200 TESS-observed exoplanets were remeasured by Han and Robertson – using software that 25-year-old Han wrote when he was an undergraduate at UC Santa Barbara – and found to be much bigger, and more liquid, than previously believed.
Those findings, in turn, suggest there might be fewer smaller, rocky Earth-like planets than recently believed.
“Our studies show that a large number of the (planets) observed are larger than their first measurements. And this reduces the population, and changes the likely frequency, of Earth-like planets,” Han said.
That said, it’s too soon to know if that reduces humanity’s prospects of bumping into extraterrestrials.
More bigger planets might mean more moons, and some of those moons could host life if they’re in the so-called “habitable” zone – not too close, not too far – from their sun. What’s more, other recent work, including discoveries by other researchers at UC Irvine, have found that tens of billions of white dwarf stars once believed to be non-starters in the search for life might, in fact, generate enough heat to make a planet habitable.
Instead of blunt questions about extraterrestrials, Han and Robertson hope their work will help lead to inquiries about how planets form, what planets are made of, and what types of atmospheres they can and can’t support.
“Astronomers are really curious about what the typical solar system looks like. Does it look like ours? What we’re finding is that a lot of solar systems don’t look like ours,” Robertson said.
“When you start to take planets and move them from one box to another, it changes what we think we know about solar systems.”
Or, as Han added, “it changes planet formation theory.”
It also means doctoral candidate Han, and 39-year-old Robertson, an associate professor – both of whom have discovered or helped discover their own exoplanets – have produced research that upends work that some of their compatriots have spent years fine-tuning. Though scientific inquiry should mean new information is always welcome, humans, even scientists, don’t always like learning that they might be wrong.
“I’m not sure everybody feels great about this. But my understanding is if we see something that shouldn’t be overlooked, we should be happy to see it,” Han said.
“I am sure they will be pleased to get more accurate results.”
The research came together quickly.
Last year, Han was testing his software by remeasuring some TESS-viewed exoplanets. When he presented the results to Robertson, Han noted that his measurements were uniformly bigger than the sizes listed in published papers about those planets. Han assumed the error might be in his software; Robertson wondered what it would mean if the software was accurate and the data about the planets was wrong.
“We were sitting around a conference table, together, when we had the initial aha moment,” Robertson said.
“We had to brainstorm what kinds of tests we could and should do.”
In November, Han began the process of reading research papers on about 230 exoplanets. He also began the process of remeasuring each one, generating hundreds of printouts of zeroes and ones. Those were eventually transformed into data showing that all but about 30 of the measured planets were, on average, much bigger, and more liquid, than previously believed.
On Monday, July 14, Han and Robertson –- along with co-authors Timothy D. Brandt, Shubham Kanodia, Caleb Cañas, Avi Shporer, George Ricker and Corey Beard – published their results.
Those results could quickly change the hunt for habitable planets.
Han noted that while his calculations aren’t “an easy fix,” they do present a path other researchers can use before they publish data about their planets. Han and Robertson also said the software isn’t a commercial product, and is being made available to the research community. They also both suggested other software might be in development that soon could leapfrog what Han has created.
Their focus, they said, is to expand what’s known – and to raise new questions – about planets outside our solar system.
Astronomers, for now, don’t even have a strict definition for what a planet is or isn’t (or for “life,” for that matter). Accurate details about the planets we’ve observed to date could lead to one.
“There has been a robust discussion about this result,” Robertson said. “Our hope is that it continues.”