Mar 162016

By Jason Tumlinson, Astronomer at the Space Telescope Science Institute

What are the most amazing astronomical discoveries in our lifetime? The realization that the Universe is dominated by dark matter? The finding that Hubble’s expanding Universe is actually accelerating? That planets orbiting normal stars are common? To me, the most amazing discovery is one that has yet to be made, but which many astronomers are spending their careers to pursue: whether or not life as we know it has arisen beyond the Earth, even beyond our own Solar System. This question was asked by the ancients of many cultures, and has preoccupied some of the deepest thinkers up to the present day. We astronomers working now are privileged to live at a time when we can foresee, and personally work toward, the day when this question may be answered.

Talk to the right kind of biologist, and you’ll find that “origins of life” research has become a respectable branch of their field, in a multidisciplinary brew of molecular and cell biology, biochemistry, genomics, and even quantum physics. Researchers in their labs have created simple genomes from scratch, synthesized self-organizing membranes to hold them, and replicated many possible variants on the primordial chemical conditions where life on Earth may have originated. Yet there is one ultimate experiment that no Earth-bound lab can ever hope to perform: has Nature replicated her experiment on Earth by giving rise to life elsewhere? This is a problem for the astronomers.

How will we do it? In short, by finding Earth-like planets around nearby stars and remotely sniffing their air. Since the discovery of exoplanets 20 years ago, and the first direct measurement of an exoplanet atmosphere in 2002, it has become routine to measure the composition of planetary atmospheres. But detecting direct signs of life on other Earths will be much more challenging than anything we can do today, chiefly because each Earth is lost in the glare of its parent star, shining 10 billion times brighter than the planet itself. If we can achieve suppression of the starlight so that the planet can be seen, we can look for oxygen, ozone, water, and methane – the signs of life.

Astronomers have now started serious efforts to find and look for signs of life with the next generation of space telescopes. The James Webb Space Telescope, launching in 2018, will excel at studying the atmospheres of “SuperEarth” planets (about 1.5-2 times Earth mass) around stars smaller than the Sun. The WFIRST mission that NASA has just begun will improve starlight suppression to within about a factor 10 from that needed to study true Earth analogs around Sun-like stars.

To truly answer the origins of life question, we need to reach statistically significant samples of Earth-like planets around nearby stars. This is a problem for a large space telescope, something still larger than JWST. One such concept was dubbed the “High Definition Space Telescope” (HDST) in a report issued by AURA last year. Another name is LUVOIR, the Large Ultraviolet/Optical/Infrared Surveyor, just now under study by NASA. In either case, a telescope of 10 meters or more in aperture will be necessary to characterize dozens of Earth-like planets and look for signs of life there.

Such an observatory also promises to revolutionize virtually every other area of astrophysics with its high resolution imaging and multiplexed spectroscopy. It should be to the astronomical community in two decades what Hubble is now – the all-purpose eagle eye on the cosmos.

In future posts I’ll expand on these themes and describe the incredible potential of such a telescope, the science behind testing “origins of life” theories with astronomical measurements, and the energizing possibilities of a 10 meter telescope in space. Please come back and see how cool the future can be!


Figure: Notional design of a High Definition Space Telescope (HDST).