A blog about exoplanets, scientific computing, and life as I know it.

The Automated Planet Finder, Systemic and Super Planet Crash

[This short article I wrote has been published on The Conversation UK.]

The following is a short article about the Automated Planet Finder, Systemic and Super Planet Crash. We recently announced the first batch of exoplanets that were discovered in the first few months of science operation of APF. The first two systems (HD141399 and Gliese 687) have been submitted and will be available on astro-ph shortly.


Telescope apps help amateurs hunt for exoplanets


Laurie Hatch

People around the world are being invited to learn how to hunt for planets, using two new online apps devised by scientists at the University of Texas at Austin and UC Santa Cruz.

The apps use data from the Automated Planet Finder (APF), Lick Observatory’s newest telescope. The APF is one of the first robotically operated telescopes monitoring stars throughout the entire sky. It is optimised for the detection of planets orbiting nearby stars – the so-called exoplanets.

Systemic is an app that collects observations from APF and other observatories and makes them available to the general public. Anyone can access a simplified interface and follow the steps that astronomers take to tease a planetary signal out of the tiny Doppler shifts collected by the telescope.

Students and amateurs can learn about the process of scientific discovery from their own web browsers, and even conduct their own analysis of the data to validate planet discoveries.

The second app, SuperPlanetCrash, is a simple but addictive game that animates the orbits of planetary systems as a “digital orrery”. Users can play for points and create their own planetary systems, which often end up teetering towards instabilities that eject planets away from their parent stars.

First catch

Despite only being in operation for a few months, APF has already been used to discover new planetary systems.

Night after night, the telescope autonomously selects a list of interesting target stars, based on their position in the sky and observing conditions. The telescope collects light from each target star. The light is then split into a rainbow of colours, called a spectrum. Superimposed on the spectrum is a pattern of dark features, called absorption lines, which is unique to the chemical makeup of the star.

When a planet orbits one of the target stars, its gravitational pull on the star causes the absorption lines to shift back and forth. Astronomers can then interpret the amplitude and periodicity of these shifts to indirectly work out the orbit and the mass of each planet.

This method of detecting exoplanets is dubbed the Doppler (or Radial Velocity) technique, named after the physical effect causing the shift of the absorption lines. The Doppler technique has been extremely productive over the past two decades, leading to the discovery of more than 400 planet candidates orbiting nearby stars – including the first exoplanet orbiting a star similar to our own Sun, 51 Pegasi. To conclusively detect a planetary candidate, each star has to be observed for long stretches of time (months to years) in order to rule out other possible explanations.

The APF has now found two new planetary systems surrounding the stars HD141399 and Gliese 687.

HD141399 hosts four giant, gaseous planets of comparable size to Jupiter. The orbits of the innermost three giant planets are dramatically more compact than the giant planets in our Solar System (Jupiter, Saturn, Uranus and Neptune).

Gliese 687 is a small, red star hosting a Neptune-mass planet orbiting very close to the star: it only takes about 40 days for the planet to complete a full revolution around the star.

Team leader Steve Vogt of the University of California, Santa Cruz has dubbed both of these almost “garden variety” planetary systems, and indeed, they are quite similar to some of the systems discovered over the last few years. However, what look like distinctly unglamorous planetary systems now can still pose a puzzle to scientists.

The new normal

The planetary systems discovered so far are typically very different from our own solar system. More than half of the nearby stars are thought to be accompanied by Neptune-mass or smaller planets, many orbiting closer than Mercury is to the Sun. In our solar system, on the other hand, there is a very clear demarcation between small, rocky planets close to the Sun (from Mercury to Mars) and giant planets far from the Sun (from Jupiter to Neptune). This perhaps suggests that planetary systems like the one we live in are an uncommon outcome of the process of planet formation.

Only further discoveries can clarify whether planetary systems architected like our own are as uncommon as they appear to be. These observations will need to span many years of careful collection of Doppler shifts. Since the APF facility is primarily dedicated to Doppler observations, it is expected to make key contributions to exoplanetary science.

The two apps produced by the APF team make amateur scientists part of the hunt. These applications join the nascent movement of “citizen science”, which enable the general public to understand and even contribute to scientific research, either by lending a hand in analyzing massive sets of scientific data or by flagging interesting datasets that warrant further collection of data.

The Conversation

2,000,000 systems played!

The high scores as of April 13, 2014 for all of posterity. Good job, brave folks.!

The high scores as of April 13, 2014 for all of posterity. Good job, brave folks!

This week has been quite the ride. Super Planet Crash has been featured on io9, Huffington Post, space.com, Motherboard, and other online publications, and it “suffered” from repeated surges of traffic from imgur. Not bad for a game hacked together over the weekend! It overjoyed me to receive emails, and pictures!, by people enjoying the game, especially from the younger generation.

More than 2,000,000 games have been played as of today, and hopefully a fraction of those players will want to know more about exoplanets. I would also encourage everyone who enjoys this little free game to donate to science education funds, such as McDonald Observatory’s Science Education Fund. I would be oh so happy to have bragging rights due to planet crashers donating en masse!


I’m slowly trying to work through some of the feature requests. Not all are feasible on a short timescale (science is my full-time job, after all!), but I will strive to at least try to address the lowest-hanging fruit. One pet peeve shared by many was the inability to see the high-scoring games. In trying to address this, I discovered two bugs in the implementation of the high-scores.

The first is that the server relied too much on trusting the high-scores that were sent from the client (i.e. the Javascript running in the web-browser). Although I had tried to mitigate it somewhat, several fake high-scores were submitted. I added some stricter checks that should further help address the problem. The right solution would be to run the system on the server in order to check for any shenanigans. Unfortunately, this is unfeasible, as too many games are being played: it would place an unduly amount of stress on my server.

The second is a bug in the way systems were recorded and sent to the server. Some of the highest-scoring systems attempt to score high on masses, “crowdedness” (how close are the orbits of the bodies to each other) and habitability. They do that by (a) adding a binary companion (the “dwarf star”) and (b) putting a lot of planets in the same orbit within the habitable zone.

 

Something like this.

Something like this.

The resulting systems are likely highly chaotic, so any small error in recording the state of the system 1 will change the outcome very quickly (the so-called “butterfly effect“). Unfortunately, one bug in Super Planet Crash resulted in this exact scenario happening. Any rounding or truncation of the floating point values for the coordinates will also affect the evolution of the system. The most common outcome is that these high-scoring systems will appear to be unstable when replayed. Grrr.

The decision I reached is to clean up the high-score table. The systems should now be recorded the correct way, and everyone will be able to see how the scores were achieved.

I understand this is sad news for the current record holders, so the screenshot at the top of this page will record the brave folks who reached upwards of 300,000,000 points for all posterity. (Just imagine someone unplugged the arcade machine by mistake…)

Next up on my agenda is releasing the game on GitHub. I am cleaning up the last few bits. If you are a programmer, you’ll be able to create pull requests for new features there.


In my next post, I will go into a bit more detail about how I created Super Planet Crash (and so can you!).

Notes:

  1. The state of the system being the current position and velocity of each body.

Go Crash Some Planets!

Super Planet Crash

A screenshot of Super Planet Crash playing in Safari


 

If you enjoyed playing Super Planet Crash, please consider donating to the Science Education Fund at McDonald Observatory. Every little bit counts. Go support science!


Update 2: 2,000,000 systems were created!
Update
: Systemic and Super Planet Crash were featured on io9Space.comGlobalNews, Motherboard, Huffington Post, The Verge, and two press releases by UC Santa Cruz and McDonald Observatory. Thank you!

Super Planet Crash is a little game born out of some of my work on the online version of Systemic. It is a digital orrery, integrating the motion of massive bodies forward in time according to Newtonian gravity. It works on any recent web browser and modern tablets.

The main goal of the game is to make a planetary system of your own creation be stable (i.e. no planet is ejected, or collides with another body). This is of course exceedingly easy when your system comprises of a few Earth-mass planets, but dynamical instability can quickly set in when adding a lot of heavier bodies (from giant planets, all the way to stellar companions).

The challenge is then to fit as many massive bodies as possible inside 2 AUs (twice the distance between the Earth and the Sun), teetering close to instability but lasting at least 500 years. Accordingly, the game rewards a daring player with more points (proportionally to the mass of each body added to the system). A few simple rules are listed under the “Help” button.

The game always starts with an Earth-mass planet in a random location, but you can also have fun overloading known planetary systems! Clicking on the “Template” dropdown brings up a list of planetary systems to use as starting templates, including the compact system Kepler-11 and the super-eccentric planet HD80606 (more systems to come). You can even share your creations with your friends by copying the URL in the “Share” box.

The game is open-source, and still under active development. The entire code will be downloadable from GitHub (as soon as I get a bit of work done!).In the near future, I will be adding integration with Systemic Live, a longer list of template planetary systems and smartphone support. In the meantime, have fun crashing planets!

Credits

The game was made possible by the wonderful paper.js library, which let me quickly prototype the app despite having little experience in web gaming. The palette draws from the base16 color set.

Many many thanks to my wonderful testers: Rachael Livermore, Mike Pavel, Joel Green, Nathan Goldbaum, Maria Fernanda Duran, Jeffrey SilvermanAngie Wolfgang, and other cool people.

My work is funded by the W. J. McDonald Postdoctoral Fellowship. If you enjoyed the game, please donate to the McDonald Observatory fund to support science education.

Funniest Software Bugs

This is a cute collection of fun software bugs from Michael Tsai’s blog: Funniest Software Bugs.

I incidentally enjoyed learning about the units shell command, a useful utility to convert between units from the command line:

stefano ~$ units
586 units, 56 prefixes
You have: 100 feet/s
You want: km/hr
	* 109.728
	/ 0.0091134442
You have: 30 J/yr
You want: erg/s
	* 9.5066294
	/ 0.10518975

(Its man page informs me that it cannot convert Celsius to Fahrenheit, since it can only handle multiplicative scale changes: boo!).  And what the heck is a fathom?

-5 minutes to Kepler teleconference!

Watch here.


Woohoo! 715 new planets in one go were announced during the teleconference.

A few screen captures:

photo 2 photo 1


knownexoplanets (1)

Arc posted two new papers (Lissauer et al., 2014 & Rowe et al., 2014) and a media kit.

exoplanetdiscoverieshistogram

Look at that histogram go!


Figure 3 of Rowe et al., 2014

Figure 3 of Rowe et al., 2014

This figure from Rowe et al., 2014 shows the incident flux (normalized to the incident flux on Earth) versus the radius of the planet (in Earth radii). There’s something interesting to be said about it, but it will deserve a blog post on its own…

Setting up a nice AucTeX environment on Mac OS X

Most people I know use TeXShop on Mac OS X. While it’s a pretty good TeX editor, I think Emacs is overall vastly superior. Of course, I’m rather biased since I already use Emacs for everything else… Perhaps this post will be useful to other Emacs-addicted astronomers.

In my setup, I use the AUCTeX package coupled with the Skim PDF viewer (if you’re not using Skim, download it, it’s brilliant!). One of the advantages of this combination is that Emacs and Skim can be kept in sync, like in the screenshot below.

Skim + Emacs/AUCTeX nirvana. Note that the current highlighted line in Skim corresponds to the cursor position in Emacs.

Skim + Emacs/AUCTeX nirvana. Note that the current highlighted line in Skim corresponds to the cursor position in Emacs.

I found it a bit difficult to set up the AUCTeX package with sensible defaults, so I’ll reproduce here my configuration in hopes that it will be useful to someone else.

The salient lines are the ones configuring latexmk and Skim. You should have latexmk installed if you are using the TeX Live distribution; Skim can be downloaded for free here. You can stick this script in your Emacs initialization file (see my dotemacs repository if you’d like to see my other Emacs configs). I shamelessly copied those lines from this Stack Overflow answer.

Two LaTeX gems: ShareLaTeX and latexdiff

Here are two really cool LaTeX tools every astronomer should enjoy.

ShareLaTeX is an online LaTeX writing tool. It’s great for collaboratively writing LaTeX documents of any size, and a life-saver when you don’t have access to your own laptop with a TeX installation on it — just grab a web browser, navigate to ShareLaTeX and write away, then grab the PDF product. (You can also chat with collaborators, browse revisions, and a bunch of other useful niceties.)

A sample ShareLaTeX project.

A sample ShareLaTeX project.

The folks behind ShareLaTeX generously announced today that they made their product open-source. Here is the GitHub page with their source code. It appears to be extremely easy to run your own local installation, if you so desire.

While working on a grant application (in the old, inefficient fashion: on a Dropbox shared folder) I wished there was some way to send “diffs” of my changes to the PDF to my collaborators, in order to save them the time to hunt for the changed word or sentence. Emery Berger’s blog directed me to the latexdiff tool, which I had somehow never heard about! It’s quite easy to install (if you use MacPorts, it’s a simple sudo port install latexdiff), and the resulting PDF diffs are nice and clear.

A sample latexdiff output.

A sample latexdiff output.