AAS 231: Day 3


Editor’s Note: This week we’re at the 231st AAS Meeting in National Harbor, MD. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume next week.

Plenary Talk: Venus: Our Misunderstood Sister (by Kerry Hensley)

Darby Dyar of the Planetary Science Institute has served as a professor of astronomy, a participating scientist for the Mars Science Laboratory, and a tireless advocate for women in science. In today’s first plenary session, she revealed the fascinating features of our sister planet, Venus, and made a strong case for continued missions to this least-explored terrestrial planet.

Though Venus and Earth are nearly twins in mass and size, evolution has separated the two siblings; Venus is an inhospitable world with a surface temperature hot enough to melt lead, a corrosive sulfur and carbon dioxide atmosphere, and only trace amounts of water. What can we learn from studying such an unfriendly place? Venus-like exoplanets appear to be roughly as common as Earth-like exoplanets, so learning about Venus can help us understand a sizeable number of exoplanets. Studying Venus is also key to understanding the Earth itself; as Venus may have once been habitable, understanding its evolution can help us understand Earth’s future.

There are also many misconceptions about Venus. The classical picture of Venus is of a dry, inactive planet that is impossible to study because of its thick atmosphere and high surface temperature and pressure. Dr. Dyar dispelled these misconceptions and painted a new picture of Venus as a dynamic and geologically active world with complex mineralogy that, though dry today, once hosted an ocean’s worth of water. As tantalizing as this picture is, our understanding of our sister planet is hindered by our lack of high-quality data. We can only learn so much from laboratory studies, as well; “Venus chambers” are difficult to build and when they fail, they fail … explosively. So, to Venus we must go!

What does the future of Venus exploration look like? NASA’s 2017 Discovery-class mission finalists included two Venus missions, while the most recent call for New Frontiers-class proposals included three Venus missions as finalists — but in neither case was a Venus mission selected. (It’s worth mentioning that in the most recent call, the mission concept VICI was selected to receive funding for further technological development.) Though there are no NASA Venus missions on the horizon yet, Dr. Dyar closed the session by declaring the Venus science community ready to explore, “…poised now with mature mission concepts, intellectual capital, and experience.” And Venus is worth exploring.

Press Conference: It’s Amazing What You Can Do with Space Telescopes (by Benny Tsang)


This artist’s illustration shows the NICER mission at work aboard the International Space Station.

Studying space is cool, but studying space from space is even cooler! Today’s morning press conference focused on the latest results from various space telescopes. Keith Gendreau (NASA Goddard Space Flight Center), the Principal Investigator of the Neutron star Interior Composition Explorer/Station Explorer for X-ray Timing and Navigation Technology (NICER/SEXTANT) mission, showed that we can build an interplanetary navigation system (aka a GPS for spaceships) by just observing pulsars. Pulsars are neutron stars — remnants left behind after the deaths of massive stars — that rapidly rotate, forming a beacon of light with clock-like regularity. NICER/SEXTANT uses X-ray telescopes on board the International Space Station (ISS) to measure the arrival time of the pulses from three or more such pulsars, from which we can deduce the spatial location. Through precise measurements with only built-in flight software within the NICER payload, the mission demonstrated that pulsars can serve as reliable navigational landmarks for future journeys in our Galaxy! [Press release]

Next up, William Clarkson (University of Michigan-Dearborn) charted the motions of Sun-like stars in the bulge of the Milky Way as they orbit. The measured motions of the stars revealed that stars with different chemical compositions follow different orbits. This finding provides constraints on the formation and evolution of the galactic bulge. The extension of the project will provide observationally verifiable predictions for how the galactic bulge formed.


Artist’s impression of high-speed jets emitted from the supermassive black hole at the center of an active galaxy. [ESA/Hubble, L. Calçada (ESO)]

Supermassive black holes live in most of the galaxies in the universe. Their masses range from a million to hundreds of millions of solar masses. It has been known that when the black holes feed on gas, they also expel energy in form of gas burps. Julie Comerford (University of Colorado, Boulder) presented a double-burp captured by the Hubble Space Telescope and Chandra Space Observatory from the galaxy SDSS J1354+1327 800 million light-years away. The presence of a companion galaxy suggests that the separate meals were likely provided by an earlier galactic collision. [Press release]

Brett Salmon (Texas A&M University) reported the discovery of a very old galaxy that existed when the universe was only 500 million years old. This galaxy, SPT0615-JD, was discovered in Hubble’s Reionization Lensing Cluster Survey (RELICS) and companion S-RELICS Spitzer program. While finding old galaxies at high redshifts is not new in astronomy, the novelty of this particular galaxy is that its images were stretched into long arcs due to the distortion of light by a cluster of galaxies in the foreground)=. Analysis of the arcs showed that the galaxy mass is only about 1% of the Milky Way, and it is only 2,500 light-years across. Salmon also noted that the advent of the James Webb Space Telescope will provide astronomers with details to further constrain the structure of the galaxy, e.g., are there rotational structures in such early galaxies? [Press release]

Warner Prize Lecture: The Evolution of Stars & Galaxies (Chris Lovell)

The Helen D. Warner Prize is awarded annually for “a significant contribution to observational or theoretical astronomy,” and 2017’s winner Charlie Conroy (Harvard University) has certainly satisfied this criterion with his work on modelling the spectra of stellar populations, known as Stellar Population Synthesis (SPS). It is impossible to resolve individual stars in distant galaxies; instead, we see the combined light of many different stars, all with different ages and physical properties. SPS modeling aims to untangle these physical properties from this combined light, and the technique has a long history, starting in the ‘60s.

In order to build a population of stars you need three “pillars”:

  • An initial mass function (IMF) that describes what masses stars are typically born with
  • Models for how these stars evolve with time
  • Models for the light they emit, or their spectra.

An important ingredient for modelling spectra is the ratio of different elements within the stars, which can have a huge impact on the spectra. The abundances of elements can in turn tell you when these stars formed, since different elements are formed in different kinds of supernovae, and different types of supernovae occur in stellar populations of different ages.

One element of SPS models that Conroy highlighted was the IMF, which is typically assumed to be universal throughout the cosmos — stars are born with the same distribution of mass no matter what the local properties of the gas, the host galaxy, or the age. But, to quote Conroy, “It’s really hard to imagine it doesn’t depend on anything”. Unfortunately, untangling any dependences is notoriously difficult. The culprits of this difficulty are the low-mass stars, which dominate the total stellar mass (because there are so many of them compared to high-mass stars) but only contribute a few percent to the galaxy’s total light. Recent measurements, though, suggest that galaxy mass is correlated with how “bottom-heavy” the IMF is (how many low-mass stars there are), and this variation is confined to the central regions of galaxies.

To conclude his talk, Conroy gave a shout-out to researchers performing atomic and molecular line modeling of the Sun and nearby stars, since it is these studies on which much of his work depends, and he made a plea for more researchers to look into this field — it could be where many future gains in SPS modeling, and in astrophysics in general, now lie.

You can read more about Conroy in Ashley Villar’s interview.

Henry Norris Russell Lectureship: Fifty-Four Years of Adventures in Infrared Astronomy (Kerry Hensley)

This year’s Henry Norris Russell Lectureship is awarded “on the basis of a lifetime of eminence in astronomical research” to Eric Becklin of University of California, Los Angeles. As a pioneer in the field of infrared astronomy, Dr. Becklin is more than deserving of this award; while most scientists hope for one or two major discoveries in their careers, Dr. Becklin introduced more than ten eye-popping discoveries that advanced our knowledge of the infrared universe.

His first major discovery came as a grad student at Caltech working with Gerry Neugebauer to complete a 2.2-micron survey of the Orion Molecular Cloud in a search for the first protostar. The pair virtually stumbled upon an extremely bright infrared object with a temperature of 600 K that had no optical counterpart — just the protostar they had been searching for. “The optical astronomers didn’t think we’d discover anything in the survey. We were just out there looking around,” he recalled, before modestly adding that the difficulty of discovering the Becklin-Neugebauer Object, as it came to be known, paled in comparison to the challenge of passing his graduate quantum mechanics course.

The infrared sky survey also led to the discovery of IRC +10216, the brightest object outside the solar system at 5 microns. IRC +10216, also known as CW Leonis, is a nearby (just 100 parsecs away), highly variable carbon star. Or, as Dr. Becklin phrased it, “A dust and carbon molecule factory in space.”

From there, his career expanded to encompass infrared observations of virtually every corner of the universe; from studying highly-extincted stars near the center of the Milky Way to taking (Congressionally-mandated!) 5-micron images of Jupiter as support for the Voyager spacecraft, Dr. Becklin has had a hand in a host of infrared discoveries. One of his most significant contributions is as the Chief Scientist for the Stratospheric Observatory for Infrared Astronomy (SOFIA), a position he still holds. (Recent results from SOFIA were highlighted in a press conference on Day 1 of this AAS meeting.) With SOFIA, Dr. Becklin has studied the gas and dust ringing the center of our galaxy, dynamics of stars orbiting the central black hole, star formation in the Orion Molecular Cloud, and an active galactic nucleus (AGN) at a redshift of z = 3.9.

An animation of the observed orbits of stars circling the supermassive black hole at the center of our galaxy. At closest approach (about 100 AU), the stars travel at 3% the speed of light. One star, S0-2, will have a closest approach in the spring of 2018. [Images/animations created by Prof. Andrea Ghez and her research team at UCLA. Data sets obtained with the W. M. Keck Telescopes.]

It was a pleasure to hear Dr. Becklin speak about his long career in infrared astronomy with such joy. He has clearly taken to heart the advice he gave his audience: Enjoy what you do, and enjoy the discoveries that will come — because they will come.

Plenary Talk: Astro Data Science: The Next Generation (by Nora Shipp)

Chris Mentzel is the program director of the Data-Driven Discovery Institute at the Gordon and Betty Moore Foundation. This means that he spends a lot of time thinking about how data science can be incorporated into scientific research. Particularly as astronomers builder better and better telescopes and collect more and more data, Mentzel emphasized that data science will become an essential part of astronomy research. 

Chris Mentzel

Chris Mentzel

This transition brings up interesting questions about how to incorporate data science into the world of astronomy. Mentzel pointed out that skills like statistics and software development are already common in astronomy, but that there is no accepted way to give credit to people who devote their time to these important tasks. He suggested that software development could be considered instrumentation, just like building a telescope.

He also raised the question of whether there should be a distinction between data scientists and astronomers, or whether all astronomers should be trained in these skills. He pointed out that this depends on whether data-science tools like coding and statistics are as essential to astronomy as something like calculus. If they are essential, then astronomers need to think about how to incorporate these lessons into astronomy education. If not, then we need to think about how to incorporate people with diverse skills into our research groups and collaborations.

An interesting question came up at the end of the talk — how can incorporating data science increase diversity in astronomy? Mentzel’s response was that first of all, requiring these courses would make it easier for people who may not have the free time to learn programming languages and statistics on their own to keep up with the evolving required skills. Second of all, data science techniques can be learned from people who apply them to different research areas. As astronomers begin to fully incorporate data science into their research they will come into contact with fields that are more diverse. There are certainly many questions that need to be resolved as we move towards larger and larger astronomical datasets. It is important that we think carefully about the decisions we make a about how the field of astronomy will evolve to meet upcoming challenges.