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NASA’s TESS Mission launched last March and began returning data in the fall. As the worthy successor to the wildly successful Kepler Mission, TESS promises great things.

And already some of that promise is being fulfilled. Astronomers have used TESS data to find exocomets, probe the atmospheres of planets we already knew about, and most recently to find possible evidence for imminent planetary destruction.

The possibly doomed planet is WASP-4b, a gas giant planet that passes in front of its host star every 1.5 days. It orbits so close to its host star that tidal interactions between the star and planet can cause the shape of orbit to vary over time, giving rise to transit-timing variations, illustrated in the video below.

Just this week, Luke Bouma, a graduate student in Princeton astronomy, and colleagues analyzed recent TESS observations of WASP-4b to see if the data show any signs of orbital variations. Not only did they find signs of orbital variation, they found that the orbital period seems to be getting shorter, at a rate of about 12 milliseconds per year, or about one jiffy every year. This about 1000 times faster than slowing of the Earth’s day due to tidal interactions with the Moon.

Variation in WASP-4b’s orbital period as reported in Bouma et al. (2019).

It’s not clear exactly what is causing WASP-4b’s orbit to change, and Bouma explores a couple of options. One idea is that WASP-4b’s orbit is very slightly eccentric and that tidal interactions between the planet and star may be causing apsidal precession, similar to effects experienced by the Moon that complicate the timing of eclipses.

Another, and to my mind more exciting, possibility is that tidal interactions with the host star are drawing the planet inexorably inward. In that case, WASP-4b may eventually be torn apart by its host star’s gravity, a fate that may have befallen many a hot Jupiter.

The great thing about both hypotheses is that they can be tested by additional observations. In fact, amateur astronomers may be able to contribute. Indeed, there is a cottage industry of amateur astronomers observing exoplanet transits, and the hardware, software, and expertise required are pretty minimal for serious amateurs.

Predicted orbital period variations (in minutes) going into the future from Bouma et al. (2019).

Bouma predicts that, over the next several years, WASP-4b’s orbital period might change by several minutes. If the period drops and then increases again (orange curves above), then the variations are likely due to precession, and the planet is probably safe against tidal decay.

However, if the period continues to drop (blue curves above), then the planet is likely doomed to tidal disruption in the next nine million years, short on cosmic timescales.

I just arrived home after a week-long visit to Aspen, CO to attend the Formation and Dynamical Evolution of Exoplanets Conference at the Aspen Center for Physics.

This conference was a cozy affair, with just over 100 attendees, and was narrowly focused on dynamical questions and approaches related to the origins and fates of exoplanet systems.

Researchers from around the world gave presentations on topics ranging from the dynamics of debris disks to observations of planet-hosting binary star systems. Blocks of presentations were punctuated by lengthy coffee breaks, when the real scientific give-and-take takes place. These interludes often give rise to groundbreaking, thesis-motivating, all-nighter-pulling research ideas.

Most of the presentations and conversations were excellent and inspiring, and I can’t do them all justice in a short blog post. So I’ll just talk about one that struck me in particular.

On Tuesday, Hanno Rein at Toronto spoke about a new N-body integrator his team has been developing in recent years, called REBOUND. This new framework may spur a revolution in dynamical modeling of astrophysical systems.

In astronomy, “n-body integration” is jargon for the numerical simulation of interactions among multiple (“n” of them) gravitating bodies. For hundreds of years, astronomers have been able to describe the orbital of two gravitating bodies quite easily, thanks to Johannes Kepler.

But as soon as you add another body to the system, there is no exact way to solve for the orbital motion of the bodies (except in very specific and limited circumstances). Even in the case of two bodies, if you want to include more complicated forces than simple gravity, solving for the orbital motion can be quite difficult.

To surmount these difficulties, scientists have turned to computer simulations to model in an approximate way the evolution of n-body systems. Although scientists have spent decades coming up with better and better models and algorithms, n-body simulations can still take a lot of computing power, and the often complicated codes can be cumbersome to set up and run. More than that, it’s often difficult or impossible for scientists to share results because there’s no good agreed-upon format for simulation output.

Rein’s REBOUND open-source code solves several of these problems at once: it employs latest modeling schemes to track orbital motions and gravitational interactions; it can be run using inside of an iPython Notebook; and it provides a uniform format for simulation output which anyone can use to re-run or re-analyze another scientists work – critical for scientific reproducibility. The iPython Notebook also provides a really neat visualization capability so you can directly watch the evolution of your astronomical system.

Time evolution of the orbits of stars in Leela’s constellation.

The code is so easy to run, in fact, that I installed and began running it immediately after Rein’s presentation. And all of its capabilities allowed me to finally simulate and visualize the evolution of a system I’ve wanted to look at for a long time – see animation at left (see here for how I created it).

I also gave a presentation on our group’s work looking at disruption of gaseous exoplanets.

And so, the combination of beautiful scenery and beautiful science made the Aspen Exoplanets conference one of the best in recent memory.