All posts by hp.osborn@gmail.com

EPIC-1166 b: a Neptune-mass planet with Earth-like density

How do planets form? Can they migrate through their solar system? What are they made of? What can modify a planet over time? Is Earth, or our solar system, special?

These are all questions that those in our field seek to answer. And there seems, to me at least, to be an easy way of figuring them out: Find More Planets.

NASAK2As last week’s news of 1200 new planets showed, the Kepler spacecraft is an excellent way of doing that. Even in it’s new and slightly more limited mode of “K2”, nearly 200 planet candidates and at least 50 bona fide planets have so far been detected.

I am involved in a collaboration between 7 European universities to search for and confirm planets in K2. So far this has resulted in half a dozen papers & planets including the 2-planet K2-19 system. Today I can add one more to that tally: EPIC212521166 b (or 1166 for short).

Finding and Confirming EPIC-1166 b

Initially, we searched the 28,000 stars observed by K2 in field 6; scouring the lightcurves with computer programmes and by eye to spot the repeated dips that might be the tiny signals of planets passing in front of their stars. A handful of candidates including 1166* stood out as promising targets, and we took those few stars to the next stage: radial velocities.

Transit Lightcurve EPIC1166
Transit Lightcurve of EPIC1166

Using the high-resolution spectrograph HARPS, we searched for the star’s to-and-fro motion that orbiting planets should create. In the case of 1166, we saw a strong signal on the same timescale as we expected from the transits.

Radial Velocities of EPIC-1166
Radial Velocities of EPIC-1166

Then, using a code called “PASTIS”, we modelled the radial velocities, the transit lightcurve and information about the star it orbits simultaneously to pin down exactly what 1166 could be. Almost unquestionably, it was a planet, which was a relief. But we can also tell the size of this planet: it has a radius of only 2.6±0.1 times that of Earth, but a mass a whopping 18±3 times our planet. Combined they give EPIC-1166 b a mass similar to Neptune but a radius more than 30% smaller.

Super-Earth or mini-Neptune?

This makes 1166 b a member of an interesting group of planets: between the size of our solar system’s largest terrestrial planet (Earth) and it’s smallest gas giant (Neptune). So which one of these does our planet most closely resemble?

Mass-Radius diagram showing EPIC-1166 compared to other exoplanets
Mass-Radius diagram showing EPIC-1166 compared to other exoplanets

From it’s density (5.7g/cm3), EPIC-1166b might seem to be closer to Earth than the puffy Neptune (1.64g/cm3). However, densities are misleading for objects so large. The high pressures in the interior of an 18 earth-mass (Me) planet are enough to crush rock and iron to much higher densities than their terrestrial values. This effect is so large that, for a 2.6Re planet to have earth-like composition (70% rock, 30% iron), it would need to be around 50 earth masses! That’s a density nearly three times higher than Earth’s, and clear evidence that 1166 b is not quite as Earthlike as first impressions.

EPIC1166_Compositions

Instead, it seems like our planet must contain something other than just rock and iron. The most obvious candidate is hydrogen gas. This is so light and fluffy that at atmosphere consisting of only 1% the mass of 1166 b (0.2Me) is enough to cover an 18Me earth-like core in a 0.4Re-deep atmosphere, and produce the mass and radius that we see. Alternatively, water could be another component that could drag the density down. For example, if 1166 b was 50% water and 50% rock, it could also explain the composition perfectly. However, this scenario is unlikely, and a hydrogen-dominated atmosphere seems to be the more likely option.

Getting a handle on the interior composition of a planet is interesting, but in EPIC-1166 b’s case it is especially perplexing. Planet formation models show that, once a planet grows to around 10Me, it should begin to rapidly draw in gas from the surrounding gas disc until it becomes a gas giant like Jupiter. In the case of 1166 b, we also have reason to think it likely migrated inwards to its current position through that very gas disc. This is because it is not close enough for tides to affect its position, and orbits in a circular (rather than eccentric) orbit; both pointers to disc migration.

So how did it avoid becoming a gas Giant? One way might be if EPIC-1166 b was a gas giant, but lost all its atmosphere due to UV and X-Rays emitted from its star. However, at 0.1AU and with a surface temperature of 600K (much less than many exoplanets), 1166 b is too far away to have been affected by activity.

impactMy favourite way of solving this puzzle (and it is pure speculation) is through giant impacts between planets. This could both grow a large planet at 0.1AU after the initial planet formation stage, and also blast away a large hydrogen atmosphere. The fact that the star is much older than the Sun (8±3 Gyr) and that we do not see any other planets in the system, further adds to the possibility that this was once a multiplanet system (like K2-19b and c), which destabilised, crashed together, and resulted in a single dense mini-Neptune.

The jury is still out on it’s precise formation. But with EPIC-1166 b orbiting a bright star, there is hope that we can re-observe the planet and tie down it’s size, composition and history even further. And, together with the diverse and growing crop of exoplanets, this new mini-Neptune will surely help to answer those important open questions in our field.

And if that fails we can always fall back on the exoplanet mantra: Find More Planets.


The paper was submitted to A&A and released onto arXiv (http://arxiv.org/abs/1605.04291) on May 13th 2016.

*EPIC-1166 b was initially (and independently) detected by Suzanne Aigraine and released on twitter.

Single Transit Candidates from K2

Our paper entitled “Single Transit Candidates from K2: Detection and Period Estimation” is out on arXiv today (and under review at MNRAS)! Here is a brief overview:

NASAK2It’s now more than a year since the Kepler space telescope renewed its search for transiting exoplanets. It has spent that time looking at a series of parts of the sky for 80 days at a time, substantially shorter than the continuous 4-year view of the original mission. However, the number of planets it should be able to spot as they cross their star remains the same. So, with K2’s limited campaigns, it should see many long-period planets that transit only once.

NumberSTEsIn fact, using a couple of different estimate for how many planets are out there, we expect to see a detectable single transit around every few thousand stars in K2. Given that it looks at nearly 20,000 at a time, there should be a lot out there to find!

But without seeing a second or third transit, there would seem no way to estimate the orbit of the planet. However, with such good in-transit data from Kepler and knowledge of the planet’s parent star from it’s colours, we can begin to estimate such planet’s orbits. To do this, I developed the transit modelling code (Namaste: An Mcmc Analysis of Single Transiting Exoplanets), which estimates the planetary velocity across the star, and uses Kepler’s laws to turn this into an orbital period. To test this code, we tried it out on six known Kepler planets, which gave extremely promising results, with orbital period estimates often within 10%!

We then had to go hunting for them in K2!To do this we ran a transit model along the curve, storing wherever it found a good. We also checked the resulting transits by eye, and found a few more it inexplicably missed along the way. The results of that were the seven dips you see below; our best single transit candidates.

K2SinglesEach of these dips could be caused by a planet crossing in front of it’s star. Alternatively, something else could be cause the signal, such as the eclipse of a star in front of another star. For three of these transits, we think this scenario is more likely, either because the radius given by Namaste is too big to be a planet, or because the period estimated is just too long. For example, EPIC203914123 gave a whopping great period of 200 years! As the probability of seeing a transit scales with distance, we are very unlikely to be seeing such a planet in transit; instead this is much more likely to be a small star crossing a giant star on a shorter orbit

coldPlanetThree more of these single transits are ambiguous – they could come either from binaries or planets. The uppermost signal, however, is exceptionally well-constrained and very likely to be a planet. We estimate that this object, which crosses the 11th magnitude star EPIC203311200, has a circular period of 540 +410/-230 days and a radius 0.51±0.05 times that of Jupiter. If it turns out to be planetary (and I’m speculating here), this would make it a mid-sized gas giant placed at the outer edges of its star’s Habitable Zone. And while gaseous planets are inhospitable to life, the possibility of habitable or even inhabited moons around EPIC203311200b cannot be ruled out.

As with all planet candidates, however, we need to do more work to confirm this hypothesis. This includes weighing the planet with radial velocity observations and searching for contaminating stars with high-resolution images of the star.

But with many similar missions to K2 (for example, TESS and PLATO) on the horizon, finding and analysing the single transits of long-period exoplanets is likely to become extremely important. It could even let us find planets that can be confirmed by the Gaia mission or future direct imaging. Alternatively, such planets could let us use JWST to sample the as-yet unstudied atmospheres of warm- and cold-jupiters for the first time.

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I should point out that this paper is under peer review and may change somewhat on publication. We decided to put on arxiv for a few reasons; the first being that, as evidenced by two candidate papers last week, K2 papers just seem to be going that way. The second being that the excellent Planet Hunters team released a similar technique for single transiting Kepler planets last week, and it felt logical to try to release them close together.

I will also be releasing the transit analysis code Namaste on my github this week (it needs a few tweaks and additions before it’s useable by anyone else unfortunately).

Looking for Life – Part I

“Why do astronomers look for Earth-like planets in their hunt for life in the universe. Why couldn’t life exist in all manner of ways that we are incapable of contemplating?”

I see this question, put in a variety of different ways, all the time. And to first glance, it is a valid question. Why should we focus on finding Earths? What if, by searching for only the ‘twin’ of Earthlife, we’re missing a plethora of friends and family? I hold the opinion that we’re not. That life formed of carbon, oxygen & hydrogen atoms suspended in water is in all likelihood the most common, and maybe the only, way that the universe is able to ‘do’ life. And that, while the habitable zone (the zone where an Earthlike planet would have liquid water on it’s surface) is not the only place in the universe that these ingredients can get together, it is both most likely and most likely to be detectable there.

So I will lay out my argument here in a series of posts that are almost certainly better explained elsewhere.

What is life?

A question famously posed by Schrödinger in the 1940s, it is also the first key question on our path: To find life, we need to know what we’re looking for…

Defining life may, to first glance, seem obvious. But the boundary between the living and the lifeless is hard to define – just ask any virologist. Definitions of life tend to focus on the fact that all lifeforms are structures capable of self-replication (ie reproduction), movement, growth, and the ability to evolve. But these properties, themselves, are not unique among the natural world. Crystals can replicate themselves and even respond to the environment. Bubbles of fat can inorganically grow and replicate. And anything capable of near-perfect self-replication is likely to feel the process of natural selection.

One of Schrödinger’s great insights about Life is that it does not die. It “evades the decay to equilibrium”, instead exchanging material with the environment to keep alive for much longer than an ordinary lump of matter might. In Schrödinger’s words, life feeds on ‘negative entropy’ (order in the environment) and produces positive entropy (in waste and heat).

But just how valid is this definition? Are we focussing too much on earth-life and leaving out a whole universe of possibilities. Could life be simple, rather than complex; electrical rather than chemical; or even gaseous rather than semi-solid? Give each point a bit of thought and the alternative, to my mind, sound implausible:

Complex – Picture an airless world covered in fine, unstable sand. One day, maybe thanks to a meteorite hit, a cavity is created and a small cascade begins, slowly eating its way into the surface like a wave. I can see this cascade steadily feeding off the gravitational energy of the raised sand, increasing entropy in the low sand left behind. It might even grow over time and then split into two or more such cascades. But is this system alive? My thought would be ‘no’, because of the final argument for life – that it must undergo evolution by natural selection. A single simple process such as this, while ticking all the boxes for life, cannot adapt. The cascade of sand is not determined by any in-built mechanics, but simply the result of disequilibrium.

There is also no easy way to turn one molecule into another and energy. Even the simplest chemical pathways have an energy barrier to get over, such that stored energy and catalysts are needed just to make more energy and avoid death. Then there is the apparatus needed to reproduce not just all that energy-making machinery, but also the structures that hold this all in one place. Life, by its very definition, seems to need to be more complex that the environment it feeds on to evolve.

Chemical – The universe has plenty of other ways of making and transferring energy, as the example above shows. But life requires not only creation of energy, but also to store and use that energy too. While electrical, thermal or even light energy could likely be used (indeed life on earth does), this energy cannot itself form its own storage facility; Light cannot conjure its own mirror. For that, it needs to interact with chemistry. Only the chemistry of complex molecules has the dexterity to perform these storage and reproduction tasks.

Semi-solid – Specifically, life must have a barrier to it’s environment. Just to avoid death and decay, all life on earth continually cycles through its own body weight in energy and resources once every day or so. This is only possible thanks to the fact that our bodies have a semi-solid barrier to the surroundings, with the molecules of metabolism able to leave by diffusion. If metabolism excreted solids (like FeS or SiO), these products would build up and suffocate the organism. If an organism were fully liquid or gaseous, all the important self-replicating machinery would drift away due to diffusion. Life needs to be self-contained, and it likely needs a liquid solvent in which to live…

I hope I’ve shown you that, by simply starting at the definition of life and applying physics, we can get a decent handle on what life in the universe must be like. It seems like that life must be more complex that it’s surrounding; it must be a chiefly chemical system and it must be self-contained. That is a surprisingly narrow conclusion, but surely there could be a myriad of ways to assemble a chemical system such that it fits the criteria for life? We shall explore that next in “The Ingredients of Life”.

 

Further Reading:

Erwin Schrodinger – What is Life (pdf version here)

Nick Lane – The Vital Question (review)

Southern Skies Above La Silla

In December 2014 and June 2015, I was lucky enough to visit La Silla in Chile. Part of the European Southern Observatory, La Silla is home to dozens of working telescopes. My baby for both occasions was the 1.2m Swiss Telescope, designed specifically to search for exoplanet via the radial velocity technique.

I also happen to enjoy photography (some of my work is here), so turned my camera to the skies most nights during both my two-week stays. This video is the result of nearly 10,000 photos taken on those trips. Hope you enjoy it! Feel free to share it far and wide.

 

Technical details:

I was using a Nikon D3200, a remote shutter (although when this broke, an elastic band over the shutter did the job), a Hama tripod and both the basic Zeiko 18-52mm lens and Sigma 12-24mm wide-angle lens. I also used my GoPro occasionally for the twilight sequences.

In total, I took around 10,000 photos totally around 200GB of photos. Exposure times were from 25 to 40 seconds and ISO levels from 400 to 1600. In total, I ended up with about 60 sequences of ~1hr in length, totaling 1.5 days of shutter open time!  The first batch (from December 2014) went on a hard-drive that later broke, so a few dozen other timelapses were lost. I used UFRaw to reduce the images convert to jpg, Panolapse to create the moving timelapses and Lightworks to assemble the video.

I’m not happy with all of the images; some have been poorly reduced, some were set at too high an ISO rate (made worse by the poor noise properties of the D3200). But this is my first (or maybe second) venture into Astrophotography, so I figure I’m allowed to make a few mistakes!

The music is Modern Drift by Efterklang, all rights for which are the property of 4AD & Rumraket (used under fair use guidelines).

EDIT: The video was, unfortunately, taken down by Vimeo for not constituting ‘Fair Use’ (I believed that a non-profit, educational video such as this adhered to Fair Use, but apparently vimeo disagree). It is now up on Youtube who have a less stringent fair use policy.

The Solar System’s has Four New Neighbors

The number of worlds discovered around other stars is now counted in the thousands. But, if you were to go out on a dark night and try to spot those planet-hosting stars with your own eyes, you would struggle – only 6% of planets orbit stars bright enough for our eyes to pick out. This is especially true of transiting planets; those that pass in front of their star relative to our line of sight. Of more than 1000 such planets known, only one (55 Cancri) is bright enough to see in the night sky. That is, until today…

Position of HD219134 in Stellarium

HD 219134, nestled between Cassiopeia and Cephus, is remarkable in so many ways. It was first studied with HARPS-N, during it’s Rocky Planet Search. This instrument, a spectrograph on the TNG telescope in the Canary Islands, is able to measure the motion of stars so precisely that it can spot the to-and-fro wobble caused by planets.

Amazingly, this instrument found not just one but four planets around this star; a mini solar system just like our own. The outermost is a gas giant on a 3-year orbit, while the inner three are between the size of Earth and Neptune orbiting once every 3, 7 and 47 days.

And the prize for funkiest Colour scheme goes to...
And the prize for funkiest Colour scheme goes to…

ssc2015-02b_Inline[1]At this point, astronomers had no idea if these new worlds transited. But a planet on a 3-day orbit has pretty good odds to pass in front of its star so, taking control of the Spitzer space telescope, they pointed it and hoped. And sure enough, exactly when predicted, the innermost planet blocked out 0.036% of starlight. This fraction is just the surface area of the star covered up, giving a precise measure of the radius of the planet.

Now, with the mass of the planet measured by HARPS and the radius of the planet measured by Spitzer, it’s density can be found. While many similar sized worlds have turned out to be fluffy gas-balls rather than true super-Earths, a density of 5.89gcm-3 puts HD 219134b bang on Earth-like composition. If there was a surface, it’s gravity would be just under twice what we experience on Earth (18.8ms-3). With an orbit of only three days, though, the planet’s star-facing surface is likely to be hot enough to melt!

HD219134dens

At only 20 light years away, the newly-discovered solar system around HD219134 is also the closest transiting exoplanet ever found, and one of the 20 closest bright star systems to our Sun. With transiting planets extremely rare, there’s even a chance that this could actually be the closest transiting planet around a bright star (K & G-type).

HD219134’s brightness is also important for astronomers. The brighter & closer a planet, the more interesting ways we can study it. For example, this new world has jumped to the top of the list for those trying to study exoplanet atmospheres. We can also measure the path it takes as it crosses it’s star to determine just how the planet orbits. The outer 3 planets might peturb the orbits of the inner one, causing detectable variations in transit timing (TTVs).

It has truly been a remarkable week for exoplanet astronomy, beginning with the discovery of habitable-zone super-Earth Kepler-452b, and now the detection of the brightest, closest, awesomest transiting planet ever found. And, thanks to a huge array of exciting follow-up options, this will not be the last you’ve heard of HD219134b,

 

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Here’s how you can find the star in the sky (and a very neat animation of the transit):

 

The paper by Montelabi can be found on arXiv here

Other coverage includes:

Elizabeth Tasker’s piece on “The closest rocky planet ever has been found… so what?

Sci-News: HD 219134: Three Super-Earths Found Orbiting Star 21 Light-Years Away

Daily Mail: Star discovered with THREE Super-Earths, and one is the closest rocky planet ever found outside our solar system Read more: 

Wasp Planets… as Pokemon: A Chrome App

Scanning the list of new planets WASP has found (a large proportion of which are unpublished), it occurred to me that we are getting very close to 150 planets! It also occurred to me while making the Underground Map of Wasp planets (see next post), that our planet names are really boring.

Pokeball
An exoplanet Transit

So, to both fix the naming problem and celebrate the number of WASP planets, I have decided to turn all Wasp planets into the 150 original Pokemon! Working on Wasp-12 b? Nope – You’re working on Butterfree. Wasp-6? Charizard. Wasp-64? Machoke. Wasp-135 b? Jolteon. IAU eat you heart out…

And while I know this will be a difficult thing to achieve politically, we can at least achieve it indirectly, thanks to the magic of Chrome Apps! Unfortunately I don’t have time to make a completely self-contained app for this, but here’s 4 quick steps to follow to add a bit of early-naughties humour to exoplanet science:

  1. Open Chrome and go here to download ‘WordReplacer’
  2. Find Chrome’s ‘Settings’ menu, then the ‘Extensions’ tab, then find ‘Word Replacer’ and click on options.
  3. Open up this pastebin in another tab, and copy the text (it’s easiest from the “Raw paste data” box at the bottom). [BONUS: Kepler names replaced by 1920s baby names with this pastebin]
  4. Back on Word Replacer, click ‘Import’ and paste the text in. Finally, click Save Settings and you’re good to go!

Then you get to enjoy lists such as this; or papers such as this: PokemonPlanets PokemonPlanets2       . . . . EDIT: Bonus update. Now replace all Kepler planet names with the top 2000 baby names… from the 1920s! Say hello to planets Gertrude (Kepler-127), Salvatore (312) and Ruth (Kepler-11). Use this pastebin in place of the WASP-only one above to get both!

Kapetyn b – Another One Bites the Interstellar Dust

A new analysis of Kapetyn’s Star by Paul Robertson at Penn State University suggests that Kapetyn b, the innermost and most Earth-like of two planets detected in 2013, is not a planet but rather an artefact of sunspots on the star’s surface.

Kapteyn_b[1]
Kapetyn’s star compared with Earth. Credit: Habitable Exoplanet Catalogue
The two planets were detected by Anglada-Escude using the radial velocity technique. This involves tracing the spectrum of the star, the light from which is imprinted with a barcode of absorption lines, to detect minute changes in the velocity of the star. The team used this to spot the to-and-fro (Doppler) motion of the star due to gravitational pull of two unseen planets.

This also allowed Anglada-Escude to place the innermost planet in the Habitable or “Goldilocks Zone”, the region around the star where temperatures might be just right for liquid water to exist on the planet’s surface.

Activity Tracer showing Rotation Signal & alias
Activity Tracer showing Rotation Signal & 48-day alias

But planets are not the only thing that can influence a star’s spectra – Robertson’s reanalysis of the spectra found tracers for starspot activity which varied on a 143 day period. This caused an artefact signal at 143/3 days, or 48 days: precisely the supposed orbital period of Kapetyn b.

This latest result is the third skirmish in a bitter war between the two teams with three habitable-zone planets detected by Anglada-Escude all now refuted by Robertson.

(paper: Stellar activity mimics a Habitable-Zone planet around Kapteyn’s Star )

Shifting Eclipses – K2’s Second Multi-planet System

On March 20th this year, the moon will pass between Earth and the Sun sending a slither of Northern Europe into darkness. For those in the UK, this partial eclipse will be the most impressive eclipse until three minutes of totality at 4:56pm on September 23rd, 2090. Calculating something so far ahead seems like an impressive feat but in fact astronomers can precisely work out exactly when and where eclipses will occur for not just the next hundred, but the next million years. Such is the way for most transiting exoplanets too, the calculations for which could probably be valid in thousands of years.

477859main_KeplerSinglePanelStill[1]But a new planetary system, discovered by a team that includes Warwick astronomers (including me), doesn’t yet play by these rules. It consists of two planets orbiting their star, a late K star smaller than our sun, in periods of 7.9 and 11.9 days. The pair have radii 7- and 4-larger than Earth, putting them both between the sizes of Uranus and Saturn. They are the 4th and 5th planets to be confirmed in data from K2, the rejuvenated Kepler mission that monitors tens of thousands of stars looking for exoplanetary transits. (36 other planet candidates, including KIC201505350b & c, have been released previously).

But it is their orbits, rather than planetary characteristics, that have astronomers most excited. “The periods are almost exactly in a ratio of 1.5” explains Dave Armstrong, lead author of the study. This can be seen directly in how the star’s brightness changes over time. This lightcurve appears to have three dips of different depths, marked here by green, red and purple dips. ”Once every three orbits of the inner planet and two orbits of the outer planet, they transit at the same time”, causing the deep purple transits.

K2 Paper Lightcurve

But this doesn’t just make for an interesting lightcurve; the closeness of these periods to a 3/2 ratio also causes other weird effects. “The planets perturb each other and change their period every orbit, so they never quite transit when you expect”, explains Arms. These shifts are called Transit Timing Variations (or TTVs).

An Example of TTVs in a 2-planet system
TTVs in a 2-planet system (credit: Eric Ford)

The size of these TTVs is related to the mass of the planets, and some previous multi-planet systems have been weighed in this way. When the team went back to observe the larger planet less than 9 months later, they found that the transit time had shifted by more than an hour. And their period ratio of 1.5035 means the resulting TTVs are likely to continue increasing over a few years, potentially shifting the system more than a day from it’s current rhythm.

These TTVs also help prove that the planets are real. Their presence means that both objects are interacting with each other, so the planets must orbit the same star rather than being, say, two different background binaries. The team also used these shifts in transit time to constrain the planet masses, showing them to be less than 1.2 and 2.04 times that of Jupiter.

rvgif2[1]Not only is this one of the most interesting multi-planet systems yet discovered by Kepler, it is also one of the brightest (12th magnitude), making ground-based follow-up much easier than many Kepler systems. Most interestingly, precise spectrographs like HARPS and SOPHIE will be able to measure the tiny to-and-fro shift in the star’s velocity caused by the gravitation pull of planet on the star. This radial velocity would give a precise mass for the planets in the system and for the first time allow masses found by TTVs to be directly compared to those from RVs.

Fomalhaut_planet_341px[1]Examples of 3:2 resonance can be found everywhere in planetary science, including between Pluto & Neptune’s orbits, in the Kirkwood gap of the Asteroid Belt, and even between the planets around pulsar PSR1257+12. It is also thought that Jupiter and Saturn may have, at one point, become caught in a 3:2 resonance as they migrated inwards. This scenario, of planets caught in 3:2 resonance migrating inwards, could explain how these two sub-Jupiter sized planets came to be in such an unusual orbit.

These two planets could also help settle other dilemmas. “We’d like to answer questions like ‘Did they form there?’, ‘Did they migrate there and get stuck?’ and ‘will they eventually get ejected from the system, or crash into the star?’” suggests Armstrong. The best way to do this is simply by watching future transits and monitoring just how in-sync the planets really are. And maybe one day we could even begin to predict their eclipses as confidently as we can with those happening here on Earth.

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The paper, submitted to A&A, can be found on ArXiV here. My work on the paper involved developing the tools to find the transiting planets in the K2 lightcurve.

A History Of Planet Detection in 60 Seconds

Last week I gave my first proper talk to a conference of PhD students from nearby universities. Being an easily distracted man, rather than actually write my talk, I decided to spend the day before putting together an animation of the entire history of Planet Detection, from 1750 to 2015. It shows the orbital period (x-axis), planet mass (y-axis), radius (circle size)* and detection method (colour) of the 1800+ planets now known.

Made by Hugh Osborn
Made by Hugh Osborn

More Details

The idea of this plot is to compare our own Solar System (with planets plotted in dark blue) against the newly-discovered extrasolar worlds. Think of this plot as a projection of all 1873 worlds onto our own solar system, with the Sun (and all other stars) at the far left. As you move out to the right, the orbital period of the planets increases, and correspondingly (thanks to Kepler’s Third Law), so does the distance from the star. Moving upwards means the mass of the worlds increase, from Moon-sized at the base to 10,000 times that of Earth at the top (30 Jupiter Masses).

The colours are also important – dark blue shows the solar system planets (which include Ceres and Pluto for a few deacades each); In light blue are RV planets, which began the gold rush in 1995 with the discovery of 51 Peg; In maroon are Direct Imaging planets; in orange the microlensing discoveries; and in green those planets found by the transit method.

You might see a few patterns beginning to emerge:

The top left has a dense cluster of large worlds. These are the Hot Jupiters. We know of loads of these, even though they’re pretty rare, simply because they are easiest to find. Being so close to their star they produce the biggest radial velocity signals (light blue) and are most likely to transit (green). Ground-based transit surveys like WASP cant find anything beyond ~15 days, causing the sparse region to the right of this group.

The top right cluster is a population of Jupiter-like worlds that Radial Velocity is best at finding – anything beyond 10 years is too long at the moment to have a full signal.

The bottom group is from the Kepler space telescope. This clustering is the only one that’s actually real and not just a systematic effect. This is because Kepler was capable of finding every type of planet down to ~1 Earth radius. So this clustering shows that there are more Earth and super-Earth sized planets than any other. Hopefully we can begin to probe below it’s limit and into the Earth-like regime, where thousands more worlds should await!

Hope you enjoy it, and feel free to borrow it for your own use!

*Where Mass or Radius were unavailable I used the Mass-radius relations of Weiss & Marcy. Information from exoplanet.eu, so it might be a bit wrong. Thanks to Matt Kenworthy for suggestions. Pulsar planets are not plotted.

Lunar Mission One – Can It Succeed?

10349900_1523807731203424_1290925223437780697_n[1]73%. That’s what former Minister for Science and Chairman of Lunar Missions Ltd Ian Taylor reckoned the chance of success of Lunar Mission One would be. This number, on the face of it, appears to be reasonably precise. Assembled from a detailed analysis of all the risks, you might think? No. In reality, like much of his talk this evening, it was a fudge – pieced together on the fly, with little scientific substance to back it up.

Lunar Mission One is a crowd-funded space mission. Started in late 2014 by a wide array of collaborating UK institutions which Ian Taylor listed with pride. It plans, in the early 2020s, to send a probe to the Moon and perform cutting-edge scientific research. They pitched the idea to the public via Kickstarter and, by the skin of their teeth, made it to the £600,000 goal needed to start developing the idea. Their ultimate goal is to produce a mission for everyone. (Where, as far as I can work out, ‘everyone’ is those who have donated sums of money to the cause).

lunar-mission-one_3110612k[1]Their scientific principle, at least, has merit. They will fly a large probe to the unexplored Shackleton Crater at the Lunar South Pole and use cutting-edge drilling tools to make a ~100m hole in the lunar ice and rock. The geology of this borehole could reveal untold secrets about the history of the Earth-Moon system and make literally dozens of British Lunar geologists quite happy.

The team will then fill in this hole with “Memory Boxes” – digitised containers that members of the public can, for a small fortune, fill with their most treasured memories and unwanted iTunes collections. These will then sit under the lunar crust for 4 billion years before either being fried by an expanding sun or rescued by some helpful intelligent alien species.

Lockheed build the Phoenix Lander
Lockheed build the Phoenix Lander

For those of you worried that there might be a limit to the market of moon-based hard-drive storage space, fear not – the Lunar Mission One team might have something else up their sleeve: Someone will take it over! Ian Taylor banded around a couple of names. Lockheed Martin for instance. For too long have these private contractors worked for contracts based on money – the time is right for them to start backing space missions for free…

Despite lots of long-winded answers-that-weren’t-quite-answers, Ian Taylor did not really fill us in on just how such a mission might be funded. The £600,000 raised so far is only 0.1% of the budget needed to get a space probe to the moon. He suggested international collaborations could easily get the funding necessary, but with most western countries already invested in their own agencies (eg ESA), where and why would any extra funding end up in a British company’s hands?

google-lunar-x-prize[1]The Google X-Prize contenders, who set to reap a $35million bonus for landing on the moon, tell a cautionary tale. Backed by a combination of crowd-funding and business investments, not one of the half-dozen teams involved made it to the Moon by the 2012 deadline. Twice this has been extended, and twice the teams have failed.

Even private investors such as Virgin Galactic or Space-X, who have a profitable business model, have struggled with the costs and timescales involved with spaceflight. And these, which Ian Taylor was so quick to draw comparisons to, are profitable ventures. Lunar Mission One has even less potential for generating income than Mars One, another independent space mission that looks destined for failure. Most would agree that crowd-funding has its limits, and £600million is above that limit. Way above.

Another question that springs to mind is why, if the scientific concept is so good, did the institutions involved go down a private route? Why not propose directly to ESA, and face the potential of €650million reward to build the space mission? I put this to Ian, and he tried to convince me that ESA (and NASA) was hell-bent on Mars and not on the Moon, whereas the scientists he had spoken to were adamant that lunar missions are more important. (NB: Well of course they were, Ian; you spoke to Lunar Scientists. If I only spoke to the dozen White Dwarf astronomers in my department then I’d probably get the idea that the only necessary mission was to send a craft to Sirius B!) And ESA missions to Jupiter, a comet, the Sun as well as two exoplanet satellites prove that is not really the case. The selection process is done by numerous committees that select programs based almost entirely on their scientific potential. That lunar geologists cannot get their missions selected in telling.

China's Moon Probe, Chang'e
China’s Moon Probe, Chang’e

In reality, most planetary scientists would agree that there are still other more interesting places in the solar to explore than the Moon. Many of these destinations, such as our planet’s near-twin Venus, are also relatively thin on the ground when it comes to future missions. The Moon, however, is an easy target for newly-emerging space agencies such as India and China. One can even imagine a manned mission before Lunar Mission One even launches.

I was cautionary optimistic when before hearing Ian Taylor and the Lunar Mission One concept. Now, after an hour of name-checking and avoiding difficult questions, I feel the opposite. The whole mission seems to lack any clear sense of direction. It seems like they caught their £600k target almost by surprise, like a dog chasing a car. Now, from that unlikely position, they must raise £599million more (£15 for every working adult in the UK) for a mission that, compared with the exploits of Rosetta, sounds uninspiring.  73% suggests Ian? My guess would be more like 0.7%.