TAEM- In your last interview in our July 2014 issue we discussed your studies concerning the question about astrobiology and the search with alien life. Since then you played a key role in the New Horizons project during the fly-by of Pluto. Please describe your role in this important project.
MS– I’ve been a mission co-investigator on this team since 1999 when we first proposed to NASA a very similar mission. NASA canceled that mission opportunity. We subsequently proposed the New Horizons mission in 2000 and were awarded the mission and funding starting in 2001. My role throughout has been planning atmospheric science for the NH mission, and now that we’re past the flyby I’m Deputy Lead of the Atmospheric Science Theme Team for atmospheric science analysis. That is one of the three science Theme Teams that are working to analyze the flyby observations. Before encounter, I worked to develop models of the chemical and thermal structure of the atmosphere so that we would have a basis for predictions of what we would see at encounter. It’s very important to have predictions, because instruments must be designed carefully to match what we general expect to see. Since the encounter, I’ve worked with others on the team to write scientific papers and give presentations at conferences on our results.
TAEM- How important is the study of this distant planet?
MS– Much more so that we thought before the encounter! We’ve found that the outer solar system is a much more complex region that we would ever have expected. Pluto is one of the Kuiper Belt objects – one of about 100,000 of dwarf planets that orbit the sun in the general vicinity of Pluto’s orbit. We expected these to be cold and dead, at least geologically-speaking. But we found a geological active Pluto with evidence for ice volcanoes, an atmosphere that undergoes climate changes that dwarf those on Earth, nitrogen ice glaciers that grow, move, and sometimes recede with the state of the atmosphere, and we now have evidence that Pluto has a subsurface liquid water ocean with perhaps more liquid water than in all the oceans on the Earth. The study of Pluto is forcing us to re-writing textbooks on all sorts of things about how planets form and evolve. We don’t know the source of the energy that powers Pluto’s geology, so we now have a bunch of mysteries on top of all the things that we do think we understand.
MS– Some of the things I noted above are rather amazing discoveries. In my own area of atmospheric science we found an atmosphere that has many features that seem to defy our models. The atmosphere has an extensive haze layer (up to about 200 km above the surface) that we are now beginning to understand as being produced by the condensation of hydrocarbons onto small particles that settle downward and ultimately coat the surface of Pluto. But embedded inside the extensive haze layer are very thin (about 1-2km) much brighter haze layers that are mysterious. We simply don’t have a mechanism to explain those layers at present. We also found that the upper atmosphere on Pluto is much colder than we expected. This is likely due to some cooling agent such as an infrared-active gas. But we can’t figure out what kind of gas is doing the cooling.
TAEM- Since the completion of the initial mission NASA has granted your team the ability to continue forward into the Kuiper Belt. How excited were you to learn of this and what future role will you play?
MS-The extended mission is a wonderful bonus to an extraordinarily successful mission. Pluto is but one of these numerous dwarf ice planets in the Kuiper Belt. And our Earth-based observations suggest that these objects are extremely diverse with different spectra (colors) indicating differing compositions, and it appears many have moons orbiting them (Pluto has five moons). Each one is probably a complex world like Pluto. But it will likely be decades before we can send another spacecraft mission to the outer solar system. So having the opportunity to visit another one with NH is like doubling the scientific impact of the mission. The object chosen is small and much further away from the sun than Pluto, so it will likely be much different than Pluto. But we won’t know how different until we get there on January 1, 2019.
MS-As I stated above, the target (currently identified as 2014MU69) is much smaller than Pluto with a diameter of less than 100 km. And we think it is much darker than Pluto. But we don’t know the cause of that different in brightness. Is MU69 covered in darker material? Does it have an atmosphere as Pluto has? Does it have active geology like Pluto? Does it have diverse terrain like Pluto? We simply know so little about MU69 that all questions are on the table. We will know much more in a little over two years.
TAEM- What is the importance of this?
MS-The objects in the Kuiper Belt are much older than the Earth, and MU69 may not have changed much since the solar system and the Earth formed about 4.56 billion years ago. So it is pristine planet-making material. From what we’ve learned at the Pluto flyby, our older ideas about how planets formed, and how they evolve, have had to be changed. We are still learning new things every day from the NH data. So it’s hard to predict what we will learn at MU69. But I suspect there are still many surprises in store for us as we learn more about the outer solar system from the MU69 flyby.
TAEM- In the June 2016 issue of the magazine Astronomy, Caltech astronomers declared the possible discovery of the illusive ‘Planet Nine’. Will the New Horizons team be permitted to join the search for this object?
MS-It’s not clear how NH can help in the search for the supposed planet. The larger telescopes on Earth are much better equipped and more powerful for detecting very distant objects.
TAEM- With the possibility that our solar system is much larger than previously imagined, is the New Horizons project destined to go further to find the unknown edge of our solar system?
MS-The NH spacecraft is powered by radioisotope nuclear material. That provides the heat and electricity for the spacecraft. But it is slowly decreasing in its output. By the mid 2020’s the energy will be so low that it can’t support the instruments that make key observations, and by 2030 it will be difficult to send data back from the spacecraft. But until then we will continue to learn much about the outer solar system. We will continue with solar wind observations as well as distant images of other Kuiper Belt objects. But I’m not optimistic that there will be another flyby after MU69.
TAEM- Professor Summers, with the great work that you have done with this project, George Mason University has risen high in the annals of space exploration. I want to thank you for this interview and the honor you have given our magazine for it. We hope that we have the pleasure of future interviews with you and other members of the scientific team at George Mason University.