Associate Professor of Astronomy Seth Redfield received a $415,000 grant from NASA in March to study the heliosphere and interstellar medium using the Hubble Space Telescope. The study will use various telescopes and spectroscopy— the study of matter and electromagnetic radiation—to investigate the composition, density, temperature and other properties of the interstellar medium (the portion of gas and dust between stars in a galaxy that exists just outside of the heliosphere). Redfield will carry out the research in collaboration with Research Professor Emeritus Jeffrey Linsky from the University of Colorado. 

The heliosphere is a bubble-like region that surrounds the sun and the planets in the solar system. It’s formed by the sun’s solar wind, a stream of charged particles known for causing the formation of the Aurora Borealis (or Northern Lights) upon coming into contact with Earth’s poles. Interstellar spacecraft like Voyager 1 and Voyager 2 must first pass through the heliosphere before exiting the solar system. The Voyager spacecraft were originally designed to study Jupiter and Saturn, but have since continued on into space to study Uranus and Neptune as well as the outer layer of the heliosphere and beyond. 

“There’s also a lot of interest in the astronomical community to build the next Voyager spacecraft,” Redfield said. “Those were built, 50 years ago or 40 years ago. We could make something faster, better, bigger, and send it out there.”

Both Linsky and Redfield are involved with a voyage known as the Interstellar Probe, a project in the early stages of development that aims to create a spacecraft more advanced than Voyager 1 and 2 that will explore the area outside of the sun’s solar system. 

“Hopefully that will be a mission that will go out two, three, four times as far as the Voyagers will be going and in this very long period mission, it’ll take 50 years maybe, we hope to get some really interesting data,” Linsky said.

At a meeting organized by the Johns Hopkins Applied Physics Lab that Redfield attended in October 2018, a panel of scientists discussed possible designs for the Interstellar Probe.

“We were thinking about all the measurements we could make and through that meeting we realized that we really needed to improve our sense of the local interstellar medium,” Redfield said. 

A deep knowledge of the interstellar medium is necessary for the Interstellar Probe team to understand the damage a spacecraft traveling outside of the solar system might undergo. In order to gain such an understanding, scientists need a map of the interstellar medium, something Redfield had been studying and working towards since he served with Linsky as a PhD student in the early 2000s. 

“What we’ve been doing is taking observations from the Hubble Space Telescope and trying to look at as many stars as we can and map out the local interstellar medium, figuring out how much stuff there is, how it’s moving, what its temperature is,” Redfield said. “We can measure turbulence in those clouds and all sorts of different things.” 

The Hubble Space Telescope, which is currently orbiting Earth, is operated by the Space Telescope Science Institute in Baltimore. Researchers can request to use the telescope by submitting proposals, which are then reviewed by various astronomers the Institute invites to evaluate submissions. Another option available to Linsky and Redfield is the ‘snap proposal,’ as Linsky described: 

“[The schedulers] often find there’s a gap; there’s maybe one orbit, which is like 2000 seconds of observation, where they can’t possibly fit anything in, so instead of just letting the telescope just sit there doing nothing, they request snap proposals,” Linsky said. “These are proposals basically for one orbit observation of a huge number of targets spread all over the sky to do whatever science you wanted to do.” 

Redfield compared the team’s work to a map familiar to many people: Google Maps.

“Interstellar probes like Voyager are going to be launched and move for space and they’re going to take measurements like every day and bring them back to us, so they’re kind of like Google street view,” Redfield  said. “If you go onto Google Maps, you’re on the street, you can see what’s immediately around you. But what we can do with the Hubble Space Telescope is give the overview of the Google Map itself.”

Specifically, Redfield and Linsky want to study how the heliosphere and interstellar medium interact. 

“There are many, many researchers who are studying the sun and the solar wind and the outer atmosphere of the sun and then there is a very large number of astronomers who study the stars and interstellar medium,” Linsky said. “These are two very large fields, but the area of overlap, namely how it is that the sun and the very local part of the interstellar medium interact with each other, is almost completely empty.”

Studying the interstellar medium poses certain challenges for researchers because it does not emit light. As Redfield explained, scientists must use other clues to piece together an understanding of the gas and dust there.

“There’s places where the light that a star admitted didn’t ever get to us because this gas and dust in between the stars has absorbed it,” Redfield said. “That’s actually the way we’re able to study this gas and dust. It’s really low density, it doesn’t shine on its own like stars do; we see it by how it affects light from other objects. It’s kind of like seeing the shadow of this material.”

As Linsky and Redfield can use the Hubble Space Telescope free of charge and won’t be purchasing any equipment for their research, they will use most of the grant money to support students in their labs.

“We’re not purchasing equipment, so the [grant money] is really generating jobs for people,” Redfield said. “When we think ‘NASA’ we often think of these big, expensive pieces of equipment that they build, which they do do, but a lot of money that NASA has actually gets back to pretty regular people working on these projects, including undergrads doing research.”