All posts for the month February, 2017

Unless you were living under a very large and heavy rock last week, you probably heard about the discovery of seven planets in the TRAPPIST-1 system by Michaël Gillon and colleagues.

Although this system was already known to host three, roughly Earth-sized transiting planets, the discovery of four more throws the door wide open for habitability – all seven planets receive the right amount of starlight from their diminutive red-dwarf host that liquid water might be stable on their surfaces.

There are so many interesting questions to explore for this system – What are the planets’ atmospheres like? How did this system of tightly-packed planets form and how do their orbits remain stable? And, of course, are they habitable?

Fortunately, concerted follow-up observations and theoretical studies can probably a lot of these questions. The fact that the planets all transit their small host star means their atmospheres are ideal for study by the James Webb Space Telescope. Strong gravitational tugs among the planets caused their orbits to change visibly over the course of the observations, so we have strong constraints on how exactly the planets interact.

The last and probably most important question is going to be a lot more difficult to answer. But since a detailed understanding of this system is likely (and probably inevitable, given the enormous enthusiasm for this system), we’ll soon be very close to answering the question of whether the TRAPPIST-1 system is habitable and maybe even inhabited.

One bit of trivia: the TRAPPIST survey that discovered this system was named in honor of the contemplative Roman Catholic religious order of Trappists, and the astronomers reportedly celebrated their discovery with a round of Trappist beer. Maybe this should be the start of a new tradition of naming new planetary systems after beers.

I had a great time talking about the August 21st solar eclipse at the Flying M in Nampa last night. A packed house asked lots of interesting questions about this unique celestial event, and I’ve posted my presentation below.

Several folks in the crowd kindly donated to our Pony Up Campaign to support additional public outreach, bringing us nearly halfway to our goal. One more week to go!

Thanks to our donors for their support, particularly Joann Mychals, Mark Funaiole, and M Lewis, as well as several anonymous donors.

Don’t forget about our public astronomy event on Friday, Mar 3 at 7:30p in the Physics Building, when we’ll have Dr. Kaloyan Penev of Princeton join us to talk about his exoplanet research. If the weather’s clear, we’ll also do some stargazing.


At the invite of a colleague, I recently visited beautiful Fort Collins CO, a mecca for beer-drinkers, and on a Saturday morning, we bounced from brewery to brewery, enjoying the local flavor.

The foudre at Funkwerks

While visiting Funkwerks brewery, I noticed an impressive barrel in the warehouse where they aged their beers – it was about 6 feet tall, 6 feet deep, and visibly ellipsoidal. It occurred to me making an elliptical barrel would take a lot more work than making a circular barrel, so I asked the tour guide about it.

She said the barrel, called a foudre, had originally stored bourbon, and Funkwerks was reusing it to flavor the beer with the bourbon-infused wood. It was ellipsoidal because that gave more contact between the beer and the barrel interior than a circular barrel.

Well, naturally, I didn’t believe her about the shape, so between sips of saison, I tried to calculate how much more surface area you got for the trouble of making an elliptical barrel. Turns out she was right.

First, to estimate the interior area of the barrel, I needed to calculate the circumference of an ellipse. Surprising to me, there is no simple way to exactly calculate an ellipse’s circumference, only approximations.

So to first order, the circumference of the barrel C = 2 π a √[(2 – e2)/2], where e is the eccentricity of the ellipse: e = 0 for a circle and gets closer and closer to one for a very elongated barrel. The area for the elliptical face of the barrel is A = π a2 √(1 – e2). The volume of beer that a barrel can hold is A times its depth, and its interior surface area is C times its depth.

For a more and more elongated barrel (e → 1), the area (and volume) gets very small (1 – e2 → 0), but the circumference approaches a finite value since 2 – e2 → 1. All this means that you can, in principle, make a barrel for which almost all the beer is in contact with the barrel’s surface, maximizing the amount of flavor it soaks up.

The Ediacaran critter Swartpuntia germsi

This trade-off between interior volume and surface area actually plays an important role in the evolution of modern animals.

Some very early forms of life, like the leaf-shaped Swartpuntia germsi which lived more than 500 million years ago, lacked a mouth or anus, and these critters exchanged nutrients and waste directly through their skin via osmosis.

The amount of food required and waste generated depend on amount of living matter inside the critter, i.e. on the critter’s volume. But the rate of exchange was limited by their surface areas, so critters that grew too large could starve or choke on the waste trapped inside their bodies.

Ediacarans like Swartpuntia solved this surface-area-to-volume ratio problem by having very thin and flat bodies to minimize their interior volumes and maximize their surface areas. Many modern animals solve this problem by having a highly fractal circulatory and digestive systems to maximize the exchange rate.

So, by using elliptical barrels, Funkwerks is not only making very tasty beer – they are taking advantage of technology developed 500 million years ago.

The Kepler/K2 Mission has revolutionized astronomy, having more than decupled the number of known and suspected exoplanets in just the last few years. Although we can extrapolate things we’ve learned from these distant planets to infer things about our own solar system, data from the mission have not impacted directly on our understanding of the solar system because the mission has not observed solar system objects, until now. For a recent paper, Jason Rowe and colleagues collected K2 observations of Neptune to look for the signatures of global oscillations in the planet.

What does that mean? All planets and stars exhibit intrinsic oscillations as seismic waves permeate their interiors – essentially they are ringing like giant celestial bells. On the Earth, detailed studies of these seismic waves have taught us loads about Earth’s interior, and the soon-to-launch Insight Mission will do much the same for Mars. We also study the Sun’s interior this way because we can watch as waves that originate deep within the Sun bounce around on the surface. For the Sun, these waves cause tiny oscillations in brightness every few minutes.

In the last decades, a lot of work has gone into looking for such oscillations for in gas and ice giants in our solar system, but aside from very cool indirect signatures in the rings of Saturn, no one has clearly detected global oscillations in the giant planets. Using the Kepler spacecraft, Rowe and colleagues set out to detect global oscillations by watching Neptune for 80 days. Unfortunately, in spite of a tremendous effort, they did not detect any clear oscillations from Neptune.

But amazingly, they were able to detect variations in brightness due to the Sun’s global oscillations. This is a little like seeing someone signaling with a flashlight by looking at a mirror in which the light is being reflected, only with the flashlight and mirror 4 billion kilometers apart.

The movie below shows the Kepler observations of Neptune as the planet meandered across the field of view. Keep in mind that the solar oscillations are VERY small, and the oscillations in brightness apparent in the movie are due to Neptune’s motion in the field, NOT due to the Sun. To see those oscillations, you’d need to be a computer.

Visited the Boise Public Library for a Teen Science Café yesterday evening to talk about the Physics Dept. at Boise State. The crowd of students and their parents were wonderful, and the presentation I gave is below.

It was a nice chance to talk about our Pony Up Campaign to support public outreach for the upcoming solar eclipse. We’re just finishing week two of the campaign, and it’s received a lot of local interest. Thanks to all our donors, especially Beverly Takeuchi and our anonymous donors.

Boise State’s research computing group is hosting a conference today and tomorrow on scientific computing. Along with several others, I was invited to give a 7-min, lightning talk about our research group‘s use of computing.

One of the research computing things we do is time-series analysis to look for new planets in data from the Kepler/K2 Mission. So I talked about the new planets our group has helped find – my talk is below.



The radii Rp and periods P of KELT-16 b, along with lots of other short-period planets. From Oberst et al. (2017).

There’s a new paper from the KELT Survey and led by Prof. Thomas Oberst from Westminster College announcing the discovery of another exoplanet in a very small orbit, nearly skimming the surface of its host star: KELT-16 b is a highly irradiated, ultra-short period hot Jupiter nearing tidal disruption.

These planets have been something of a puzzle since the first was discovered back in 1995. Like Jupiter, they are mostly made out of hydrogen and helium gas, but unlike Jupiter, they orbit very close to their host star, which probably means they didn’t form where we see them today.

Even among hot Jupiters, though, KELT-16 b is an outlier. It’s one of a handful of hot Jupiters with orbital periods less than 1 day (as compared to Jupiter’s orbital period of 12 years), so whatever processes led to its origin are cranked up to 11 for KELT-16 b and its ultra-short period siblings.

The mystery of its origins aside, its short period means KELT-16 b is probably a good candidate for follow-up observations of its atmosphere, particularly by the James Webb Space Telescope. But tidal interactions with its host star means it may get eaten by its host star in less than a million years, so we need to get those observing proposals submitted soon.

Dear Astrophiles, we’re officially one week into our Pony Up campaign to raise money to support outreach for the solar eclipse in August this year. Things are going great – we’re 20% of the way to our goal of $5k.

Thanks to our many donors and especially to Pam Robbins, Mark & Sharon Johnson, flying m coffeegarage, Scott Watkins, Paul Collins, Cindy Hall, Barbara & Clay Morgan, and several anonymous donors.

To celebrate our progress so far, I’ve arranged for Comet 45P/Honda-Mrkos-Pajdusakova to pass by the Earth this weekend. You can see Comet 45P in the constellation Hercules high in the early morning, eastern sky. It will look like fuzzy bluish-green ball with a fan-shaped tail. The green color comes from glowing carbon gas.


A solar sail.

Very neat paper this week from René Heller and Michael Hippke exploring the exploration of the recently discovered planetary system around Proxima Centauri.

Proxima Centauri is the closest star to the Earth (only 4 lightyears away), and last year, an Earth-sized planet was found around it, opening to door to the very real possibility of a mission to an exoplanet.

After the planet’s discovery, the Breakthrough Starshot project proposed using solar sails and lasers to accelerate a tiny spacecraft to the system. Weighing only a few grams, the spacecraft could be accelerated to 20% the speed of light, giving a travel time to the system of about 20 years. Of course, the drawback to such a short trip is that the spacecraft would quickly zip past the planet, so the mission would have only seconds to collect data.

Building on that idea, Heller and Hippke pointed out that, as long as you didn’t mind waiting a little longer to get there (about 100 years), you could send the spacecraft at a low enough velocity that the solar sail could be used to slow the spacecraft on the other end. That would give you years to collect data, instead of seconds.

Key to their solution is the idea that you could slowly turn the solar sail, similar to tacking in the wind, to optimally slow and steer your 10-gram spacecraft. The animation below shows the basic idea.

With such a small spacecraft, there wouldn’t be a lot of room for moving parts to turn and orient the solar sail. To solve this problem, Heller and Hippke suggest the sail could be made of nanocrystals-in-glass whose reflective properties could be tuned to torque the spacecraft using the stellar photons themselves.

Of course, there are still zillions of technical problems to solve for such a mission (not to mention the difficulties of obtaining centuries-long NASA funding), but this study adds one more piece to the growing possibility of interstellar exploration.