#merav opher

[txchnologist]

Voyager Nearing Solar System Escape-But How Will We Know?

by Matthew Van Dusen

Dr. Merav Opher, a Boston University astrophysicist, is waiting patiently for a supremely distant radio signal to tell her everything has changed.

Someday soon—maybe weeks or months—the Voyager 1 spacecraft will send back data that will tell scientists it has left the solar system. The little 1,592-lb. probe will be the first of two working deep-space craft to cross our system’s boundary, called the heliopause, and report back from interstellar space.

When it does, Opher, a member of the Voyager science team and an expert in how the solar system interacts with nearby interstellar space, will be one of the first to know.

Merav Opher: No, but when we saw the press release, a lot of The Voyager team folks started saying, “Oh, this is happening.” And then I emailed [Voyager project scientist] Ed Stone and asked him, “Should I announce something?” He said, “No, we’re not there yet.” This is the kind of bet that we have, we discuss among ourselves what is going on.

Txch: Do you have any idea when it will happen?

MO: I won’t even try to put a date on it. But based on my own models, we are very close—very, very close. If the data starts behaving like I think it’s doing, it is again telling us that we are very, very close.

I’m organizing a session at the end of the year at the [American Geophysical Union (AGU)] and I keep thinking maybe we’ll be able to announce it there. I’ll keep my fingers crossed. It’s that close, I think. This is all based on my models, which are not that accurate.

Txch: What sort of changes in the data will you see when Voyager 1 leaves the solar system?

MO: This is a big debate between my colleagues and me. We had a conference in Switzerland a couple of months ago and we will have another one in the fall called “What Signatures We Will See When We Are Crossing The Heliopause.” So, what we are going to see is not clear. It’s a bit of a guessing game.

The magnetic field inside the solar system points in a specific direction—it’s like a spiral. Outside the heliopause, the field is definitely not pointing in the same direction; we know it’s not a spiral. One clear signature we have left would be if we see a big rotation in the magnetic field direction. If we see something that dramatic, we’re out. But magnetic field data is very noisy and very hard to analyze. There is really only one person who can analyze it, so it takes a long time until we get the data.

That’s why we’re also looking at data from energetic particles. They are good messengers of what’s happening, so you can usually tell the story before you measure the magnetic field. They travel farther and faster so if you want to know before we get there, usually the particles can tell you.

When we crossed the termination shock, which is that region where the solar wind slows from supersonic to subsonic, we thought the data signature would be very clear, but it wasn’t. As Voyager approached, there were puzzles that made us question whether we were really there. That experience is making everyone a bit weary.

Txch: You said the air was “frothy” out there with plasma bubbles. Did that affect when you thought Voyager crossed the region?

MO: Definitely. All our ideas so far are based on old models of what happens at these distant boundaries. It’s still widely debated by my colleagues and not completely accepted in the community whether the region is frothy. The paradigm is changing so much and we are looking for signatures to really declare what’s happening.

If this theory is true, one thing that could happen is that particles that come from outside the heliosphere would have an easier time entering, so you would be sitting within this bubble and suddenly you’re looking at an enhancement of cosmic rays. This is what Voyager has seen. There is a big increase.

So, we think that this boundary with these bubbles is permeable. If you see drops of water in a permeable boundary, you will see those drops before you get there.

Txch: You could start detecting cosmic rays long before you’ve crossed through?

MO: Right. Those particles will penetrate, but the questions are how much and how quickly will they penetrate? It makes sense within our scenario if the heliopause is more permeable and lets the rays come in much easier. We still don’t have quantitative numbers and don’t know exactly how they will increase. We’re still trying to get our heads wrapped around that but, qualitatively, it seems to be going in that direction.

Txch: Is it possible there will be disagreement between scientists about when Voyager escapes?

MO: Yeah, most definitely this can happen. In 2003, there was disagreement about when Voyager crossed the termination shock. It was only announced a year and a half later when people agreed. Usually, the team tries to come to agreement, and I think this is what will happen here. I don’t think there will be an announcement without the whole team agreeing. There will be a meeting to go over the data and everyone must agree that we crossed.

Txch: Once Voyager crosses, will data coming back be able to tell you how much cosmic radiation can penetrate the heliopause?

Txch: Once Voyager moves into the interstellar medium, is there anything more to learn?

MO: There are some limitations because no one ever imagined that Voyager would go this far. There are some instrument limitations to study certain questions we would like to in this environment. But we know very very little about the interstellar medium and we’ve never been there before.

What is the level of turbulence in the medium? There are a lot of theories that think that it’s very turbulent. We’ll be able to measure the magnetic field directly. Where do heavy ions come from and in which direction do they flow? Even with limited instrumentation, Voyager will be able to answer questions like these.

Txch: Do you have champagne on ice for when everyone agrees that Voyager enters interstellar space?

MO: That’s a good idea. Maybe I should bring one to the AGU conference and have it in my pocket just in case. [Laughs.] There’s also the 35th anniversary of the Voyager mission in September and I plan to celebrate.

Top image: Courtesy NASA.

Matthew Van Dusen, Txchnologist's editor-in-chief, was a reporter for ten years at newspapers in Wyoming, Indiana and New Jersey, where he covered health care, the government’s response to Hurricane Katrina in Mississippi and government corruption. He is the former co-editor of Green Energy Reporter but is not Dutch. He tweets @matthewvandusen.

[txchnologist]

Bubbles at the Edge of Space: Merav Opher Is Changing Astrophysics

By Txchnologist Editor

In the yellowing photograph from the late 1970s, two twin girls, their astronomer father, and a young friend stand beneath the dish of a radio telescope outside São Paulo, smiling and waving at the camera. At a NASA press conference last year, the physicist Merav Opher, who had been one of the twin sisters in the picture, shared it to convey—with her typical exuberance—how deep her passions for space science run. Not long before the photo was taken, the two Voyager spacecraft had embarked on their long journeys past Jupiter, Saturn, and the other giant planets. Today, that little girl from Brazil has grown up and used data from those probes to revolutionize concepts about the edge of the solar system.

“The edge of the solar system” is more than a turn of phrase. A tenuous, invisible wind of ionized gas billows off the sun at a million miles per hour, carrying with it the sun’s magnetic field. It does not radiate out infinitely: far beyond Pluto’s orbit, this solar wind abruptly slams into the thin interstellar medium and the scattered gaseous remnants of exploded stars. That border defines what astronomers call the heliosphere.

Just a few years ago, Opher played a key role in explaining why the heliosphere is unexpectedly lopsided and off-kilter. Now an assistant professor in Boston University’s astronomy department, Opher is interpeting data that suggests that part of the heliosphere’s edge may be a churning magnetic froth, which could have broad implications for astrophysics.

“She’s had a huge impact on this outer heliosphere field,” remarks James F. Drake of the University of Maryland, a physicist who collaborated with Opher on the most recent work. “When she was starting out, most people didn’t really think the interstellar magnetic field itself did much. I think Merav played a lead role in convincing people.”

That description might have gratified Opher’s parents. “They raised us to think, ‘If you’re going to work in any field, just make a mark,” she recalls. “‘Really try to do something that matters.’"

New York-Haifa-São Paulo

Merav and her fraternal twin sister Michal were born in 1970 to a pair of expatriate New Yorkers living in Haifa, Israel. Her father, Reuven Opher, was at that time an astrophysicist at the University of Technion. Yet a sabbatical to Brazil led to her father falling in love with that country. When she was eight years old, they moved to São Paulo, where he had taken a position at the university.

She still rhapsodizes over São Paulo, which she calls a “very sophisticated, incredible place.” Brazil’s multicultural environment also helped the Ophers blend in, even though they continued to speak Hebrew at home. “Brazilians are super nice,” she says. “It’s not a place where you don’t feel welcome.”

In college Opher first thought she might become a film director. Then in her third year she fell in love with physics and put herself on a path to earn both a bachelors degree in physics and a Ph.D. in plasma studies.

Plasmas and the magnetic fields that animate them became the common threads running through all of Opher’s work. She thinks she was drawn to the subject because she knew she could never master it. “Plasma is complex,” she says. “I knew it was something I could not get my head around easily. I would have to work at it.” She adds, “I felt this was something larger than me. It was scary, but I liked the fear.”