All posts for the month July, 2015

Artist's conception of Kepler-452 b. From

Artist’s conception of Kepler-452 b. From

Exciting discovery reported last week of a planet a little bigger than Earth orbiting a star very like our Sun.

The planet, Kepler-452 b, was discovered by the Kepler mission and has a radius 60% larger than the Earth’s. It receives about 10% more light from its star than we do here on the Earth, and it’s probably about 2 billion years older. Together, these qualities mean it may be the most Earth-like exoplanet found to date (although there are lots of other similar planets).

Unfortunately, the host star is so distant, 1,400 lightyears from Earth*, that the usual method for directly estimating the planet’s mass, radial velocity observations, is not feasible. Instead, the planet’s discoverers constrain the planet’s mass by considering a range of compositions, calculating the radius expected for each of those compositions, and comparing it to the observed radius. Based on this analysis, they estimate at least a 49% probability that the planet is rocky, like the Earth.

Based on the amount of light it receives from its host star, there’s a good chance Kepler-452 b is habitable. This means, given a long-list of assumptions about the planet and its atmosphere, liquid water would be stable on its surface. Thus, Kepler-452 b joins a short but rapidly growing list of planets that might host life.

With our success finding potentially habitable planets, it’s probably only a matter of time (maybe just a few more years) before we find a planet that’s not just habitable but inhabited. Children in school right now might be the first generation to grow up in a universe where they know we’re not alone.

Today’s journal club attendees included Jennifer Briggs, Hari Gopalakrishnan, and Jacob Sabin.

*This website is the only reference I can find that gives the distance to Kepler-452 b from Earth. The paper itself doesn’t say 1,400 light years. The catalog gives a stellar magnitude V = 13.7 (also not given in the discovery paper). Converting that V magnitude to a flux and then using the stellar parameters given in the paper, I estimate a distance of 2,400 light years.

The recent study has removed Lord Helmet's original skepticism about buckyballs as the originator of DIBs.

The recent study has removed Lord Helmet’s original skepticism about buckyballs as the originator of DIBs.

At journal club today, we discussed the recent paper from Maier and colleagues which has solved the long-standing mystery of diffuse interstellar bands or DIBs.

These light absorption features were originally discovered by Heger way back in 1919, only a few months after the end of World War I. Their discrete absorption peaks are pervasive throughout visible wavelengths, indicating they are not simply due light-scattering by interstellar dust. The fact that they appear unchanged no matter the nature of the star whose light they absorb also suggests they don’t arise from the star itself. Instead, they must lay somewhere in the vast space between the Earth and the star.

Astronomers proposed DIBs might arise from dust grains, carbon chains, and even floating bacteria. Bucky balls, large soccer-ball-shaped carbon molecules, had also been proposed as candidates since they were discovered in white dwarf stars.

But deciding which candidate was actually the culprit required meticulous and highly sensitive lab work to recreate the extreme conditions of outer space, where temperatures are near absolute zero and gas pressures can be 10 million times smaller than at Earth’s surface. After twenty years of work, Maier and his team in Switzerland and Germany finally managed to create a little pocket of interstellar space in their lab.

By carefully ionizing buckyballs and introducing them into a cold He gas, they showed the spectral features created by the buckyballs in association with He matched almost exactly the spectral features of some DIBs.

The upshot of this is that the spectral forest of DIBs found at other wavelengths likely points to the prevalence of other large and complex molecules self-assembling in space, so this discovery is just the tip of the chemical iceberg. It has even been suggested that the complex molecular precursors for life originated in interstellar space in the same way as the buckyballs.

Whether that’s true or not, this discovery shows that the vast and lonely spaces between the stars aren’t quite as empty as they seem.

Journal club attendees included Jennifer Briggs, Emily Jensen, and Tyler Wade.

As the only planetary scientist at Boise State, I was asked to present on the New Horizons mission to the Math REU program here, so I put together the presentation below.

After a cram session to prepare for the talk, I opted to have the mission PI Alan Stern present the mission himself and incorporated a really great NEAF talk he gave last year.

Here are the New Horizons links I give at the end of the talk:

Thanks to Drs. Scheepers and Babinkostova for the invitation to speak.

At journal club, we discussed the discovery of two new hot Jupiters using data from ESA‘s CoRoT mission, with the names CoRoT-28 b and -29 b. Both systems seem a little off.

The host star CoRoT-28 has an inflated radius, suggesting it is ancient and on its way off the main sequence. But it has a lot more lithium than we’d expect for an old star, and its rotation rate is similar to the Sun’s, much faster than we would expect.

Equally puzzling is the transit light curve for CoRoT-29 b (shown below at left). Most transit curves are u-shaped, but CoRoT-29 b’s is strangely asymmetric. The asymmetry resembles what has been seen for a planet transiting a rapidly rotating star — rapid rotation reduces the gravity at the stellar equator, resulting in a cooler, darker region. Barnes et al. (2013) looked at the transit light curves for such a Kepler system and actually used the light curve to study the planet’s orbital inclination.

(left) CoRoT-29 b transit light curve. (right) Planet transiting star spot.

(left) CoRoT-29 b transit light curve. (right) Planet transiting star spot.

But CoRoT-29 doesn’t appear to be a rapid rotator. So instead Cabrera et al. suggest that perhaps the star has a large, nearly stationary star spot and that the planet transits the spot over and over again. However, this scenario would require a nearly stationary spot with a very long lifetime (~90 days), neither of which is expected.

So a few more astrophysical conundra to add to the growing list of puzzling exoplanet discoveries.

Journal club attendees included Jennifer Briggs, Emily Jensen, and Hari Gopalakrishnan.

Cover of the book 'The Signal and the Noise' by Nate Silver. Published by The Penguin PressJust finished Nate Silver’s book The Signal and the Noise, only a few years after it was published.

I enjoyed most of the book, especially the philosophical discussion behind it: observations of the world inherently involve uncertainty, so predictions based on those observations must incorporate those uncertainties. But as more data pour in, we should be humble enough to revise our models and predictions.

As a whole, the book was easy to follow and didn’t get too technical, giving simple, worked examples of how to apply Bayes’s Theorem, for example, to evaluate the probability that a positive result on a mammogram actually means a woman has breast cancer.

For my money, the chapters on baseball and chess were the best. I learned that in the 1997 rematch between Garry Kasparov and Deep Blue, Deep Blue pushed a pawn on the 44th move, apparently baffling Kasparov. Silver suggests Kasparov “concluded that the counterintuitive play must be a sign of superior intelligence” and lost his nerve, resigning the next game even though it could have been played to a draw. Turns out the move may have been a last-ditch, random choice by Deep Blue.

The book falls a bit short in other chapters, though. Prof. Michael Mann, famous climate scientist at Penn State, had some pretty strong criticism for the climate change chapter. I found the concluding chapter a little platitudinous, without a lot of the interesting technical discussion in previous chapters.

Still, a really engaging read and, like me, hopefully readers come away with a strengthened commitment to scientific skepticism.

A computer model of an hexagonal lipid-DNA complex. From

A computer model of an hexagonal lipid-DNA complex. From

Special biophysics seminar today hosted by my fellow prof. Matt Ferguson and presented by his former postdoc advisor Ralph Nossal on subtle changes in the properties of lipids as a function of temperature.

Dr. Nossal reviewed research by himself, Dr. Norman Gershfeld, and others going back to the 40s showing how the physical properties of lipids, including surface pressure and diffusivity, depend sensitively on their temperatures. Diffusivity, for example, for many biogenic and synthetic lipid solutions peak at very specific temperatures.

What’s so special about those temperatures? Nossal pointed out that they correspond very nearly to the body temperatures of the organisms in which the lipids are found. So this subtle behavior could be the result of biological tuning of the lipids to optimize their chemical behavior in their host organisms.

Artist's conception of a hot Jupiter shedding mass.

Artist’s conception of a hot Jupiter shedding mass.

At journal club today, we discussed a recent paper by Valsecchi et al. (2015) that looks at mass loss from hot Jupiters. These planets are so close to their host stars that the stars can blast away and rip the planets’ atmospheres apart.

By employing the sophisticated star/planet evolution model MESA, Valsecchi and colleagues found that the planets can shed most of their atmospheres, leaving behind a small sub-Neptune planet in a short period orbit. However, gravitational interactions between the planet and escaping gas actually push the planet away from the star as the planet is shedding mass, potentially out to orbital periods of a few days.

The upshot of this is that, based on these calculations, the recently discovered population of small ultra-short period planets probably did NOT originate from atmospheric stripping of more massive planets. So it’s not totally clear how these little planets originated, although Kevin Schlaufman suggested one still viable possibility.

Today’s attendees included Jennifer Briggs, Emily Jensen, Charlie Matthews, Jacob Sabin, and Tyler Wade.

restless_rocks“Tucked away in California’s Death Valley National Park, the flat basin known as Racetrack Playa is littered with stones that seem to migrate across the landscape. But how do they do it? Brian Jackson describes how he and collaborators Ralph Lorenz and Richard Norris solved a long-standing mystery.”

Thanks to Ralph and Dick for their help with this article. It was a lot of fun to write.