Studying the heavens to understand the Earth
EL I Z A BETH Ta sker bu i lds worlds for a liv ing. She’ll ta ke a sta r, scatter a “protoplaneta r y d isk ” of ga s a nd dust around it, set it spinning, and obser ve what pla net s coalesce a nd how t hey a rra nge t hemselves in orbit.
She does this in the form of computer models she creates as an associate professor at the Institute of Space and Astronautical Science (Isas), part of the Japan Aerospace Exploration Agency ( Jaxa). She is also the author of a fascinating book called The Planet Factory.
Her work sheds light on how the Earth and its solar system formed, and helps make sense of the more than 4,000 exoplanets that have been discovered elsewhere in the galaxy in recent years.
“T he f i r st exopla net was discovered in t he 1990s,” she said in an interview at her Isas office in Sagamihara, Kanagawa prefecture.
It was reported in a newspaper that “would have been sitting on my parents’ kitchen table while I was growing up [in Britain] . . . In that time, we went from not actually knowing if our solar system was the only one in the universe [to having found planets] around binary stars [and even] planets with no star . . . There’s probably bajillions of worlds out there”.
But one thing we haven’t found yet – as Tasker very much wants you to understand – is a second Earth.
Beginning with Basic
“I liked computer games as a kid,” Tasker said, describing how she got i nto prog ra mming with a simple Amstrad 6128 computer. “Its operating system is the Basic programming language, so even to run a ga me you had to do ver y simple programming.”
She learned Java and Fortran while studying theoretical physics at Durham University, and then got a PhD in computational physics at the University of Oxford.
“Nowadays I’m coding in C and Python, largely. But just writing a script that does something is really cool . . . You build your own universe.”
Tasker’s parents are also scientists, but it was pure coincidence that they gave her a name with the initials ET, something she was indignant about as a child. “It wasn’t until years after I became an astrophysicist that I realised it was kind of cool.”
Her career has taken her around the world.“I’ve done research work in America and in Canada and Australia before coming to Japan.”
In 2009, she applied for a four-month fellowship at the Na t i o n a l A s t r o n o m i c a l Observatory of Japan in Mitaka, Tokyo.
Tasker went to Japan again in 2011, to teach physics in English as an assistant professor at Hokkaido University. “I stayed there for five years. And it was great. Sapporo is a beautiful city. The snow is very exciting. Even living in Canada I have never experienced so much snow.”
She did a lot of English-language writing for t he universit y, and began look ing for a job in which writ ing would play a n even bigger pa r t. “I ca me dow n to Ja x a t h re e yea rs ago t his October. I’ve worked wit h severa l of t he different missions, but most especia lly wit h t he Hayabusa 2 mission [to t he asteroid Ryugu] . . . I do the Hayabusa2 Twitter feed, I help tra nslate our press releases, and I a lso, wit h our mission manager, write art icles.”
Ta s ker ’s big ge s t w r it i ng project so fa r is The Planet Factor y. Among concepts its readers will learn about is the ice line – t he distance from a sta r beyond which ice ca n for m i n a protopl a net a r y disk.
“It i s most commonly believed that the Earth would have formed inside the ice line [where water is rare], and therefore probably formed dry,” Tasker said. This makes the origin of Earth’s water an interesting question.
A likely answer is that asteroids from beyond the ice line occasionally got knocked out of their orbits and ended up crashing into Earth, bringing ice with them. Hayabusa2’s mission to Ryugu may provide evidence on the matter.
“I f [ a s t e r o i d s ] h a v e n’t changed much since the start of the solar system . . . then they are sort of time capsules from that very early period. So by looking at Ryugu we can see what might have showered down on the early Earth, what might have been delivered to us in terms of water and maybe organic [compounds],” Tasker said.
If long-ago asteroids had not delivered ice, Earth might be a waterless desert today. Conversely, if more such asteroids had arrived, Earth might be submerged in a global ocean. Tasker cautions that we don’t know yet if a similar water-delivery process happened for Earth-like planets in any other star system.
Tasker is part of the team behind Earth-like (build.earthlike.world), a website where you can build planets of your own by choosing numerical values for three variables – ratio of land to ocean, degree of volcanism, and position within the temperate zone.
The temperate zone, also known as the “habitable zone”, is the range of distances from a star at which a planet might have liquid water.
Apply ing your numbers to a pla net ot her wise identica l to Eart h, t he site generates a model planet. The results range from freezing worlds to scorching ones.
Tasker pointed out that real planets would be diverse in many other ways, such as chemical composition. For instance, if a world had vastly more carbon than ours, “you might get a crust that was graphite. And if you were temperate enough to have any kind of liquid it would probably be tar. So, really nasty”. Also, the atmosphere might be carbon monoxide. On the bright side, there might be volcanoes that spew diamonds.
“Just imagine the diversity that could be out there. So can we stop calling an Earth-size planet Earth 2.0, please?”
Hayabusa2 collected samples from Ryugu this summer, and it now has a long journey back to Earth ahead of it.
A future Jaxa mission Tasker looks forward to is a probe of the moons of Mars, which will also bring back samples. This too might shed light on our own planet’s origins.
“I think some of the missions that Jaxa are doing are absolutely on point for the questions that everyone wants to ask right now,” Tasker said.
“Where did our water come from? Where did our life come from? Are we ever going to find a habitable planet? And the only answer to that is if we understand how our own [planet] formed . . . The reason I work here is, this is where the answers are going to be found.”