Dr Paul Hertz, Director, NASA Astrophysics Division
Scientists are still seeking answers to questions about our universe that were posed thousands of years ago. In the first of a two-part series, Dr Paul Hertz discusses some of the latest discoveries about our universe and the missions that will help us better understand black hole populations, the evolution of the universe and life on other planets
Could you describe the responsibilities of NASA’s Astrophysics Division, of which you are Director?
The Astrophysics Division provides the direction and leadership for all of NASA’s astrophysics missions, including the planning, building, launching and operating of them. It is also responsible for the development of the science technology needed to make such missions happen. The Division conducts a basic research programme, which makes use of all the remarkable data that the missions bring back. At a higher level, the Division stewards the nation’s capabilities to perform space astrophysics, so that missions such as the Hubble Space Telescope and the James Webb Space Telescope (JWST) can be launched.
The study of exoplanets is one of the Division’s areas of focus. How will these investigations help to shed light on the formation and evolution of our solar system? What have you discovered in this field so far?
The main thing that has been discovered, in my opinion, is the diversity of planetary systems around other stars. I suppose that, in the back of our minds, we all expected that we would see planetary systems somewhat similar to our own solar system, with rocky planets near the sun and gas giants further away from it; that is not at all what we have found. In fact, we have not yet found solar systems like our own. We are finding really strange things: Jupiter-sized planets in orbits much closer than Mercury to their star; planetary systems around double stars; planets that are sharing orbits around their stars; and planets that form in one part of their solar system and then move over time, ending up with orbits in different parts of their solar system. So we are learning a lot about the diversity and evolution of solar systems and that is going to help us answer the Copernican question as to whether our solar system is typical, or unique.
I think our most exciting discovery is that Earth-sized planets appear to be very common around other stars. Based on the results of the Kepler mission, I believe that, within the next couple of years, we will answer the question as to whether habitable planets (Earth-sized planets at the right distance from their stars to have liquid water on them) are common around other stars. The question we have not answered yet is the question we built Kepler to answer: are habitats for life common in our galaxy?
It is widely cited that a greater wealth of high quality data is required in order to develop our understanding of the Universe. What kinds of discoveries could such data foster? Which areas of data currently need significant improvement?
The Decadal Survey gave us a number of different indications as to the kinds of data and measurements that we should work on next.
Of highest priority was a wide-field near infrared survey of the sky, which would enable us to characterise dark energy. The same survey would allow us to study planets around other stars that are far away from their stars. We would also be able to study the pollution of our own galaxy by looking at the gas, dust and the nebulae within it.
The Survey identified that a time series of the sky is an important area of data that we do not currently have. That is, to be able to take a snapshot of most of the sky every night to study how the Universe changes on very high timescales. It was recommended that we build an observatory that could collect gravitational waves to observe what happens at the closest distances around black holes where the light does not get out but the gravitational radiation – actual shaking of the fabric of space-time – gets out. In addition, we need to build an observatory that can study X-rays at high enough sensitivity and resolution to enable us to map the structure of space-time near black holes.
It is also a very high priority to have an observatory capable of collecting data that allows us to characterise the planets around other stars. Currently, we are just detecting them and conducting statistical surveys to find out how many there are, their size and where they are located. What we would really like to do is to be able to measure their content, look at their atmospheres and their oceans and to be able to see what they are made of.
It would be very exciting to be able to do all of those things; we are only limited by our budget.
Which missions are currently being developed by the Astrophysics Division for future launches? What are these upcoming missions hoping to accomplish?
In June, we launched the Nuclear Spectroscopic Telescope Array (NuSTAR) which detects hard X-rays similar to medical X-rays; the Universe gives these off in some really interesting places. For instance, we will be able to see smothered black holes because the X-rays can get out of the gas and dust around some of these. Previously, we have not seen them because longer wavelength-visible and infrared light cannot get out, so this mission will allow us to better understand the black hole population of the Universe. This is also the wavelength in which brand new atoms that were created in supernova explosions decay so they give off hard X-ray radiation. We will look at some of the young supernova remnants and be able to detect some of the iron and other heavy elements that were created during supernovas. This will help us to confirm our theories on how the elements of the Universe are created.
In 2014 or 2015 we will partner with the Japan Aerospace Exploration Agency who are launching a mission called Astro-H. We will provide the main instrument for the mission – the Soft X-ray Spectrometer (SXS) – to conduct tomography of black holes by looking at the X-ray emission from individual atoms that orbit them. By looking at their speed and brightness, we will be able to map out the region around black holes.
We are currently in the process of choosing our next Explorer Mission; there are two missions competing for this, both proposing to study planets around other stars. The first would perform a survey of the nearest stars to us and find the planets around them, which would help us to learn about the nearest exoplanets. The other proposed mission would be able to study the atmosphere of some of the largest and brightest planets that we know of around other stars. Next spring, we will decide which of these missions will be launched in the 2017 or 2018 timeframe.
Finally, of course, the JWST is launching in 2018 and that will be the next large observatory that NASA launches as a successor to Hubble. The JWST will observe the very first stars and galaxies in the Universe and help us understand how the Universe of today evolved from the chaos that it was after the Big Bang.
What are the Astrophysics Division’s future aspirations? By what means will these be achieved?
We would like to discover Earth-like planets around other stars and then determine whether they have life on them; we cannot do this today, but that is a goal for 20 to 30 years from now. This would be achieved by deploying space telescopes that are large enough to be capable of discovering those planets (which we are working on now), characterising them and then searching them for life. We have to do the research here on Earth to help us to understand what exactly to look for and how to tell if a planet around another star has life on it, because we are not going to be taking pictures of trees and the animals roaming about, but rather using very indirect methods as we are many light years away. Building space telescopes and conducting laboratory research is part of our long-term goal.
The second thing that we would like to do is to better our understanding of the Universe that we live in by making sure we understand the fundamental forces and the elementary particles that underlie the space-time of the Universe. We would like to complete our understanding of how galaxies, planetary systems and life come about, as we currently have just an outline of that. It is important that we look at the details in the Universe and that requires more powerful space telescopes than we have now.
Every time we launch a new observatory with a specific purpose, it usually discovers something totally unexpected that is even more exciting than what was originally planned. Hubble has done this over and over. Opening up our eyes to things that we do not know are out there is always one of our aspirations.