Senior Astrophysicist, Harvard-Smithsonian Center for Astrophysics
What is your field of study?
I’m concentrating on the high-energy aspects of stars and how those effect their environments. Stars like the Sun, fairly normal stars, actually exhibit very energetic phenomena that we don’t see with the naked eye.
An example of this is something we sometimes hear about in the news today—coronal mass ejections from the Sun hurtling towards the Earth, causing geomagnetic storms and aurorae. Coronal mass ejections are produced by magnetic fields on stellar surfaces and are essentially high-energy processes. The solar wind itself is a high-energy process, a stream of plasma coming from the Sun at about 500 kilometers a second and impacting the Earth’s magnetosphere.
How is the understanding of these energetic phenomena related to the search for habitable planets?
Energetic phenomena from stars are now understood to be vital for making planets within the disk of gas thought to surround all newly born stars like the Sun, and are probably crucial for the way planetary atmospheres evolve. Planetary atmospheres are heated and puffed up by energetic radiation from their star, and can be eroded by interaction with the stellar wind. This and the evolutionary path of the atmosphere as it interacts with the underlying planet, is a vital part of determining whether a planet is habitable.
So, my research in the last several years has been trying to understand the energetic phenomena themselves and also the impact on the environment, both the natal disk of gas in which planets form, and also more recently on the planetary environment. And it’s through that connection that I entered the Life in the Cosmos vein.
What is the Life in the Cosmos initiative?
I became interested to know, especially when the Consortium announcement of this opportunity came out several years ago, whether there were any other Smithsonian scientists that might be interested in trying to understand the more holistic approach to the Earth’s history. You know, astronomers look at the history of how the Sun has been working. Planetary scientists look at what’s happened on the Earth through time. Paleontologists, biologists, paleobiologists look at how life has evolved. And in a sense, it’s all connected. The one single overarching problem is how has the whole system evolved. And it’s not clear that you can separate out what’s happened with life on Earth from the astronomical effects.
In 2012, you organized the conference of Life in the Cosmos, supported by the Consortium for Unlocking the Mysteries of the Universe.
We have experts in most of the fields that are required to start to answer these questions, and it struck me that if we could all collaborate we could begin to address questions that we couldn’t on our own.
That was the motivation for the Life in the Cosmos Conference in 2012. We gathered Smithsonian people who were particularly interested in these problems and got outside experts to give us other perspectives and expertise. We had an extremely fruitful two-day conference.
We had biologists talking to astrophysicists talking to paleobiologists talking to atmospheric physicists talking to geophysicists. In such a multidisciplinary conference like this one, it’s natural that people don’t know about all the different fields being addressed, and that generated an extremely open and honest discussion, and we made some interesting progress. It was a remarkable event, really.
So, what came out of the conference? What were the next steps?
There were a number of ideas that came out of the meeting, some of which are being actively pursued, others of which are still on the back burner.
Just to touch on two of these, it became clear on the second day of the meeting that there was an important question regarding phosphorus, which underlies all current cellular biology as we know it and is absolutely crucial to how life on Earth developed. Phosphorus is replenished by geological activity, largely plate tectonics and recycling of the Earth’s crust. And so, out of that meeting we devised a pilot study to try and understand what would happen to life on Earth, or life on another planet, when phosphorus wasn’t so abundant.
In another effort, we’re currently writing a proposal to study how volatile elements are assembled in planets and how elements that are crucial for life can get assembled in a protoplanetary disk. Once a planet forms, you may still not have the right mix of elements needed for forming life. So it’s not a simple problem.
So, how will understanding these basic processes for creating life help in the search for life on other planets?
In astronomy today there’s a vigorous activity in searching for planets around stars. When we see these planets and their characteristics—how far away they are from the parent star, what their mass might be—we can theorize whether or not conditions may be suitable for development of life as we know it.
For example, the work on protoplanetary disks is attempting to understand what conditions are necessary in order to form a habitable planet in the first place. We need to understand the processes that make those conditions right—a very, very complex problem astrophysically and also from a planetary science perspective.
Once we think we can understand those conditions, then, there are secondary aspects. Does the planet behave in the right way to sustain life if life develops on the planet? Is there tectonic activity that can produce and sustain nutrients? How does the atmosphere of the planet behave and evolve over time? Is it something that’s always going to be able to sustain life or is it going to undergo some catastrophic evolutionary path that will render it essentially uninhabitable over a period of time?
For example, there’s evidence of a warm, wet Mars three billion years ago, which could’ve been a planet capable of sustaining life. Present-day Mars is another matter, however, since it’s a very dry planet that seems to have lost nearly all of its water. We need to understand how a planet evolves, what produces plate tectonics, how the atmosphere evolves. It’s a very multidisciplinary interlinked problem that needs to be attacked from many different angles.
What is the likelihood of life being found on another planet, and what do you think that life would be like?
We now know that there are more planets than there are stars in the galaxy, and there are at least 100 billion stars. There are certainly planets that are in habitable zones, defined as planets that should have surface temperatures that can sustain liquid water. So, now we’re looking at a situation in which there are a huge number of planets that are in habitable zones around stars. To my mind, I think it is almost certain that there will be some form of life somewhere else in the universe, and possibly even in our galaxy.
If we do detect life on other planets, the first signs that we’ll see are going to be from very primitive forms of bacteria, like life on the early Earth. And what we hope to be able to see are atmospheric modifications, the sort of biogenic signals of bacterial life changing or maybe oxidizing a planet’s atmosphere, like what happened on the Earth.
How do you think people would react to finding life on another planet?
Suppose we find some signature that we think is of biological origin on another planet. That will have a reasonably profound effect, but it’s probably just going to be another very big news item that is reported worldwide and talked about a lot on late-night television. There will always be other scientific explanations for the data that do not require a biogenic explanation.
However, detection of a signal that could only come from other intelligent life would be a history-changing moment—the moment when humans realize that we’re not alone. If that ever happens, it will be absolutely game changing—for science, philosophy, religion . . . everything.