Category Archives: Project updates

Proxima b is our neighbor… better get used to it!

It is true. We are convinced that there is a planet orbiting Proxima now. The evidence goes as follows : a signal was spotted back in 2013 on previous surveys (UVES and HARPS). The preliminary detection was first done by Mikko Tuomi, our in-house applied mathematician and his Bayesian codes. However, the signal was not convincing as the data was really sparse and the period was ambiguous (other possible solutions at 20 and 40 days, plus a long period signal of unknown origin). We followed up Proxima in the next years but our two observing runs were 12 days, barely sufficient to secure a signal which ended up being 11.2 days. So the Pale Red Dot was designed with the sole purpose of confirming or refuting its strict periodicity, plus carefully monitor the star for activity induced variability. We got very lucky with the weather so we obtained 54 out of 60 observations. The photometric monitoring telescopes (ASH2 and several units of Las Cumbres Observatory Global Telescope network), worked flawlessly so we could see the effect of spots, flares and rotation of the star, which also had a footprint on the spectra. However, nothing indicated that spurious variability would be happening at 11.2 days.

This plot shows how the motion of Proxima Centauri towards and away from Earth is changing with time over the first half of 2016. Sometimes Proxima Centauri is approaching Earth at about 5 kilometres per hour — normal human walking pace — and at times receding at the same speed. This regular pattern of changing radial velocities repeats with a period of 11.2 days. Careful analysis of the resulting tiny Doppler shifts showed that they indicated the presence of a planet with a mass at least 1.3 times that of the Earth, orbiting about 7 million kilometres from Proxima Centauri — only 5% of the Earth-Sun distance.
This plot shows how the motion of Proxima Centauri towards and away from Earth is changing with time over the first half of 2016. Sometimes Proxima Centauri is approaching Earth at about 5 kilometres per hour — normal human walking pace — and at times receding at the same speed. This regular pattern of changing radial velocities repeats with a period of 11.2 days. Careful analysis of the resulting tiny Doppler shifts showed that they indicated the presence of a planet with a mass at least 1.3 times that of the Earth, orbiting about 7 million kilometres from Proxima Centauri — only 5% of the Earth-Sun distance.

So that’s basically it : the Pale Red Dot campaign also detects the same period, and confirms that the signal has been in phase for the 16 years of accumulated observations. This is a requirement for a proper Keplerian orbit. Features like starspots are more short lived plus affect the velocities in the time-scales of the rotation of the star, which is now confirmed at ~83 days.

The combination of all the data produces this periodogram

detection_periodogram

which leaves little doubt to the reality of the signal. The peaks in a periodogram tells us where a significant period is spotted, plus give us information about its significant. The horizontal lines correspond to False Alarm Probabilities of 10%, 1% and 0.1%. Our signal is now well beyond that. The probability of a statistical false positive is smaller than one of ten millions!

So what we know? We know the period and the size of the radial velocity wobble. From that we derive a minimum mass of 1.3 masses of the Earth. With the period and the mass of the star, we know it orbits at 5% of an astronomical unit (this is 20 times closer than Earth is from the Sun), which combined with the luminosity of the star tells us that the planet is warm and can currently support liquid water on its surface. Beyond this, all is mostly speculative. But one can do simulations and educated guesses. If you want to learn more about them, follow forthcoming articles at

www.proximacentauri.info

and a contributed one to this website by Rory Barnes.

We had a press release event at ESO today. We want to thank everyone for the passion and effort shared in this project, including the Breakthrough Starshot foundation and its chair Pete Worden for giving us their support. We hope to reach the stars, there is a foundation to promote technological advancements, and now we have a target. The sky is the limit!

Peer review — or how an experiment becomes scientific literature

What is happening now?

Now that the data collection and  analysis are complete and the results written in a paper, the next step is for the paper to be verified by the scientific community before going public. Peer review is the process the scientific community uses  for quality control of results. While a new exoplanet or supernova might have little impact on our immediate life, mistakes in some scientific disciplines (eg. biomedical research, chemistry, climate change,.. ) can have very serious consequences. Requests for research funding, patents, space missions and even new medicines are generally not accepted unless they rely on publicly available, peer reviewed research.

An important component of the peer review process are the scientific journals. Some journals will publish anything as long as it is scientifically correct, while some others will only publish results that are deemed novel or represent a very significant advance.

Who decides what it is correct and significant?

For each paper, there are at least two key people that are responsible for assessing correctness and significance. They are the editor and the referee(s). To understand how peer review works, it is better to explain the life cycle of a scientific paper.

Flow chart of the peer review process.
Flow chart of the peer review process. The approximate status of our paper as of July 1st, is marked with the red dot.

Submission

The authors must choose to submit their paper to a journal of their choice. Once the journal receives the manuscript, a scientific editor is assigned to it. This editor manages and supervises the process. Editors are respected senior scientists that work full-time for the journal, or work at a University and part-time for the journal. Papers can be rejected at this stage because the editor considers there is not sufficient original science in the result, or because the article does not match the philosophy of the journal.

Paper sent to review

After a preliminary quality assessment, the editor will search for experts to provide a more detailed revision.  These experts (called referees) are scientists not involved in the result but are experts in the field to which the paper relates. One or more referees can be assigned to a paper, and they are asked to submit a report within a  few weeks.

Referees’ opinions have a lot of leverage over the fate of a scientific result. Since referees are likely to be working on a related topic, conflicts of interest can arise and it is the editors job to carefully monitor the process. For example, if a reviewer is exceedingly enthusiastic, aggressive (or even careless), editors can search for additional referees or ignore a review. Referees are asked to follow strict ethical rules and confidentiality. The identity of the referees is not revealed to the authors to protect their independence.

First revision

After a while referee reports are sent to the editor and s/he then decides whether or not to proceed with the publication. Passing first revision is an important milestone because serious show stoppers are often identified at this stage. If the referee reports are not negative, the editor forwards them to the authors, and they are given some time to address comments and criticisms. Typical requests consist of providing additional data, analyses, adding references to previous work, and providing better discussion on obscure points of the original manuscript.

This is where we are with our Proxima paper!

After implementing the changes, the authors re-submit the article together with responses to the referee reports. The editor forwards all this information to the referees, and the process is iterated until the editor accepts it.

Acceptance

At acceptance the editor has become convinced that the paper meets the quality standards of the journal. They then write an acceptance notification which is met with great delight by the authors.

We hope to reach that point soon!

… but it is not over yet

Acceptance only concerns the content. At this stage authors might need to remake plots, prepare final tables and even rewrite some small parts of the paper. This process is done in collaboration with the production teams of the journal and can take from a few days to a few weeks. Final editing is performed in collaboration with professional writers who take account of English language and style.

As in any other professionally published work, the last editorial step consists of sending the paper in its very final format (commonly called  ‘galley proofs’) to the authors for their final approval. When this is done, a publication date is assigned and the peer review process is complete.

…hooray!

Scientific results can also be presented in conferences or other media, but these are not considered valid references unless they are published in a peer review journal. Alternative peer review procedures are being tested, but still the vast majority of scientific production goes through this classic peer review system.

… reaching the public!

It is becoming increasingly important to raise awareness of new scientific (peer reviewed) discoveries, and to be clear of what they mean to all of us. Scientists often don’t have time nor the skills to do that, so this falls into the hands of outreach, press offices, science writers and science communicators in general. When a significant result is achieved, the information needs to be transformed from the dry rigour of a scientific paper to something non-specialised audiences can digest. This includes the so-called general public, but also companies, governments and policy makers who might need to decide on crucial matters based on the most updated evidence.

So, if you are a scientist and once the paper is accepted for publication, it’s a good time to contact your outreach department and work together on how to best bring the new results to the public.

Farewell, Pale Red Dot #1

The Pale Red Dot team now goes back to their daily duties. A research paper has been written and submitted to a research journal. The review process can take anytime between a few weeks to a few months. Fingers crossed! The web articles and posts in social media will remain available for your enjoyment.

A second phase of Pale Red Dot project might start soon, with more articles and further details on what the data tells us. Do not delete us from your favourite lists just yet!

Cheers, and don’t forget to look at the sky from time to time!

all

Pale Red Dot team

Science and edition; Guillem Anglada-Escude (editor-in-chief), Gavin Coleman, John Strachan (QMUL/UK), Cristina Rodríguez-López, Zaira M. Berdinas, Pedro J. Amado (IAA/Spain), James Jenkins (UChile/Chile), Mikko Tuomi (Herts/UK), Christopher J. Marvin, Stefan Dreizler (U.Goettingen/Germany), Julien Morin (U.Montpellier), Alexandre Santerne (CAUP/Portugal), Yiannis Tsapras(Heidelberg/Germany).

Support; Matthew McKinley Mutter (English language editor, QMUL/UK), Predrag Micakovic (web & IT support, QMUL/UK), Silbia López de Lacalle, Ruben Herrero Illana (Editorial support and spanish translations, IAA/CSIC), Radek Kosarzycki (media partner, polish translations)

Observatories; Oana Sandu, Lars Lindberg Christiansen, Richard Hook (European Southern Observatory, Education and Public Outreach Department), Edward Gomez (LCOGT.net, Scientist & outreach officer), Nicolás Morales (Research scientists, SPACEOSB-San Pedro de Atacama Celestial Explorations)

First half of the Doppler data

Now that we have collected 1/2 of the observations with HARPS, LCOGT.net, and ASH2, let us share a glimpse of how the HARPS Doppler data looks. As seen in the article ‘The signal’, we expect some variability of a ‘few’ meters per second, but not larger than 4–5 m/s, otherwise the UVES survey would have spotted it. Unfortunately, we cannot disclose the real data to avoid biasing the future revision of the manuscript. Instead, we present you with a few examples of Doppler measurements similar to those we are obtaining on Proxima Centauri. These are simulated datasets using the same HARPS observation dates as in the Pale Red Dot Campaign, and they reproduce the three most likely outcomes of these first thirty measurements. But there is a twist! One of the six data sets actually corresponds to the ‘real’ observations… can you guess which one it is?

Case 1 – Radial velocity variability dominated by random noise

Case1_random_dominated
Figure 1 – Left panels shows possible Doppler measurements, the central one shows one of the tools used to spot possible periodicities and the right panels show the best fits to the data once we fold it into the most favoured period in the central panel. We cannot spot any significant enough variability in these two sets. Image credits : Guillem Anglada-Escude/PaleRedDot.org

The left panels in Figure 1 show two examples of typical datasets that only contain random noise. The vertical small lines on each point are called error bars, and illustrate how uncertain each measurement is (~1 m/s). Note that depending on weather conditions some measurements have larger error bars. The central panel shows a graphic called a periodogram. Periodograms tells us which are the most significant possible periods in the data and allows us to quantify whether or not a signal is strong enough to be detected. In this example we set the detection threshold at a false alarm probability of 0.1%. That is, peaks over the blue dashed line would correspond to signals with false alarm probabilities smaller than 0.1%. Neither of these two datasets reveal a significant signal.

Case 2 – Hints of a signal, but corrupted by activity

Figure 2 – Eyeball inspection suggests there might be coherent variability but it cannot be distinguished from stellar noise. The Keplerian fits on the right don’t look great either and require orbital fits with high eccentricities, which is characteristic of spurious variability. Image credits : Guillem Anglada-Escude/PaleRedDot.org

Here we show two datasets that contain a possible Doppler signal, but these have been corrupted by non-periodic stellar activity. As in case 1, neither of the sets is sufficient to confirm a signal. Accumulation of data over the campaign should boost true planet candidates above the detection threshold, while pushing down the significance of the spurious ones. In cases like these, we would try to model stellar activity using photometry and other spectroscopic measurements to see if part of the variability could be explained by stellar noise. As an example of techniques used to achieve this, see the interview to Prof. Suzanne Aigrain.

Case 3 – A signal is well detected despite stellar activity

Figure 3 - In this two cases, signals stands out over the threshold and the right fits look a bit better, Note that these sets only contain 1/2 of the data and are barely above threshold, so even in this case we would need to wait until the end of the run and the photometric monitoring to see if their significance improves. Image credits : Guillem Anglada-Escude/PaleRedDot.org
Figure 3 – In these two cases, significant Doppler signals stand out over the threshold,. Image credits : Guillem Anglada-Escude/PaleRedDot.org

In this case we have two simulated data-sets with bona fide planet signals that clearly dominate over the noise (Figure 3). This would be the best case scenario for the Pale Red Dot campaign. Still we would need to investigate the photometry and other activity indices for activity related variability.

Thanks for following!

‘The Signal’

The campaign is up and running! As of February 9th 2016, we have only lost two nights on HARPS due to weather, which means we have 15 good qualityspectra ready for processing. On the photometric follow-up side, the LCOGT telescopes have been obtaining good data (photometry in UBV bands), and the ASH2 telescope has already accumulated 19 nights of good photometry as well (visual and red colours). The BOOTES station is suffering technical difficulties that we hope to sort out soon. Fortunately, the ASH2 telescope (the last one to join the effort, but the most successful photometer so far!) offered a degree of redundancy that saved the day! We will introduce all the observatories involved in forthcoming posts.

Feb8
Status update of the observations. We recently reached 25% of the HARPS data, and two photometric follow-up observatories have been operating nicely over the same period. We expect more downtime due to weather, but the survey goals will probably be achieved if we can hit 80% of the planned observations.

Now that we also had the opportunity to read about the Doppler method and how stellar activity can mimic the presence of a planet, let’s talk about what we are trying to achieve here. Analysis of previous campaigns show that a possible smooth signal was observable when monitoring the star at moderately high cadence; but we must remain cautious because stellar activity can produce the same kind of variability. As described in the article by Paul Gilster, Proxima has been monitored for small planets before. The most exhaustive works include the UVES/ESO survey for rocky planets around M-dwarfs, conducted between 2000 and 2009; the searches with HARPS by the Geneva team; and recently obtained data from our own high cadence program with HARPS, called Cool Tiny Beats(2013-2014). Here are some of the technical details for those of you who are interested in them…

The VLT/UVES Doppler data, and possible signals in it

The UVES Doppler measurements were published in Kuester & Endl 2008. In previous posts (eg. see Figure 1), we have seen that if we have a planet we should see an oscillatory motion over time. These measurements didn’t look much like that (Figure 2). Still, the velocities of UVES seemed to be not completely random.

Example of measurements (in red) overplotted on the expected Doppler signal caused by an exoplanet on the Star. Changes in the velocity of the Sun-like star 51 Peg used by M. Mayor and D. Queloz to infer the presence of a gas-giant planet in a short period orbit around the star.
Figure 1. Example of measurements (in red) overplotted on the expected Doppler signal caused by an exoplanet orbiting a star. Changes in the velocity of the Sun-like star 51 Peg, used by M. Mayor and D. Queloz were used to  infer the presence of a gas-giant planet in a short period orbit around the star.
Doppler measurements of Proxima from UVES. No clear sinusoid can be spotted by eye, which already rules out the presence of long period gas giants around the star.
Figure 2. Doppler measurements of Proxima from UVES. No clear sinusoid can be spotted by eye, which already rules out the presence of long period gas giants around the star.

Stars are only visible for a few months of a year, so that could be the smoking gun of a planet with a period similar to Earth that we happen to be sampling at more or less random moments of the orbit. Kuester & Endl 2008 had reasons to suspect that this variability was indeed caused by activity, or even some unknown instrumental effect. Once that possible signal was removed by fitting a sinusoid to it, very little remained in the residuals besides apparently random noise at the 2-3 m/s level. The Doppler signal of a planet is stronger if the planet is closer to the star (as in the Solar System where Mercury takes less than three months to circle the Sun, the motion of close-in planets is faster). So, while no clear signal could be extracted from these measurements, the data did tell the researchers that no large planets were orbiting the star with periods shorter than few hundred days.

Limits to the minimum mass of planets orbiting Proxima. Concerning the 'Habitable Zone' (here marked in green between 4 and 15 days, but new models suggest it extends to periods as long as 27 days), planets down to 3 Earth masses (minimum mass) were ruled out by the data.
Figure 3. Limits to the minimum mass of planets orbiting Proxima. The ‘Habitable Zone’  is marked in green between 4 and 15 days, but new models suggest it extends to periods as long as 27 days. Planets down to 3 Earth masses (minimum mass) were ruled out by the data. Extracted from Endl, M.; Kürster, M. 2008 A&A

The minimum masses of planets ruled out by UVES are illustrated in Figure 3. Let us note that we say ‘minimum mass’ of the planet because the Doppler method only measures the motion along our line of sight. Even in that case, statistical arguments indicate that it is highly unlikely to find any planet less than ~5 times the mass of the Earth in its habitable zone, with other techniques. With this upper limit set, the UVES program stopped observing Proxima and another handful of M-dwarf stars at the end of 2008.

The HARPS/Geneva team observations of Proxima prior 2012

During the same years, Proxima was observed about 25 times with HARPS. While the star did show variability at the 2-3 m/s level, it also showed evidence of activity in occasional flaring events, and some excess of radiation coming from its chromosphere. In any case, the measurements were consistent with those of the UVES survey in the sense that no obvious signal was detectable above ~2 m/s. In 2013, the star was again observed in the extended HARPS survey for M-dwarfs led by the ex-Geneva astronomer X. Bonfils, now based in Grenoble, but no report has appeared on significant period variability so far. So these campaigns led to no convincing evidence of a signal.

Doppler velocity measurements by X.Bonfils and his team taken between 2002 and 2009 with HARPS. Source : Bonfils et al. 2013 A&A, available via arXiv.
Doppler velocity measurements by X.Bonfils and his team taken between 2002 and 2009 with HARPS. Source : Bonfils et al. 2013 A&A, available via arXiv.

The ‘HARPS – Cool Tiny Beats’ observations (2013-2014)

In 2013, the same team as  the Pale Red Dot campaign started a programme to measure radial velocities at high cadence (focused on a small sample of very nearby M-dwarfs) to hunt for short period planets, pulsations and understand the connection of stellar activity with apparent Doppler signals. Proxima was a natural target for the survey, which was executed in two runs of 12 nights each (May 2013-Jan 2014). As opposed to the rest of the stars in the sample, the radial velocity measurements of Proxima were smoothly varying over both observing runs. Unfortunately, given the length of both runs, the strict periodicity of the variability could not be verified. Worse than this, the long term Doppler variability found by the UVES survey was still present but seems rather unpredictable, meaning that combining the data from years ago did not help much in confirming it. This is when Pale Red Dot was conceived…

Doppler measurements of Proxima obtained in 12 consecutive nights in May 2013, suggestive of smooth variability on the timescale between 10 and 20 days. The origin of this 'signal' is what the Pale Red Dot campaign is trying to figure out. Image credits : G.Anglada-Escude.
The top panel contains Doppler measurements of Proxima obtained in 12 consecutive nights in May 2013 which are suggestive of smooth variability on the timescale between 10 and 20 days. The lower panel is what we call a ‘periodogram’, which is a mathematical tool to identify possible periodicities in the data. Because the observing run was limited to ~12 days, we cannot really constrain the putative period with this data only. The Pale Red Dot campaign is trying to figure out if this is a strictly periodic signal feature by observing the star ~60 nights in a row, thus covering several cycles of the putative signal, and comparing the variability with simultaneous photometry. Image credits: G.Anglada-Escude.

So while we are convinced there is a signal in the Doppler measurements of Proxima, previous data do not allow to confirm its presence and clarify its origin. The long term variability of Proxima spoiled our attempts to combine data from previous observations so we needed a dedicated campaign.

In summary

Combination of UVES and HARPS data at different cadences suggest that the star is showing a smoothly varying Doppler signal. Since the UVES survey set an upper limit between 2-3 Earth masses and if the signal is not activity induced, it must correspond to a planet smaller than that (between 1-2 Earth masses>). The signal might well be caused by stellar activity, which should be quasi-periodic as opposed to the strict periodicity of the orbital motion of a putative planet. So this is what we want to figure out! If you really want to learn more, feel free to any member of the Pale Red Dot team!

What is the exact plan?

We are following Proxima Centauri for about two months. If the planet is there we should see the velocity of the star going up and down between 3 and 5 times depending on the precise period. Simultaneously, we are monitoring Proxima with telescopes from LCOGT.net, the ASH2 Atacama telescope and the BOOTES network. The contiguous and regular sampling of the observations together with quasi-simultaneous photometry should allow us to model its long term variability better and, hopefully, confirm whether the Doppler signal is caused by a planet or not. If it isn’t…  we will move on and keep searching for #palereddots around other nearby stars…

Thanks for following!

Launch!

… so you hope to find a pale red dot?

Yes! We think there might be a small planet orbiting our nearest stellar neighbor -an M-dwarf star called Proxima Centauri-, but it might also be magnetic activity. We will observe Proxima for two months with the planet hunting machine HARPS and two networks of smaller telescopes. Such monitoring should leave little doubt about the nature of the Doppler signal but… wait a second!

Doppler signal ??@#!… what is that? A magnetic M-dwarf star, is it a rock band? For two months? that seems long and boring! Can’t you find planets any other way? Shouldn’t we do it from space? How long before we can go to these planets?…

To answer this and many other questions, palereddot.org will feature articles from prominent scientists worldwide discussing extrasolar planets, the search for life beyond Earth, instruments and plans, and what we think about life, the universe and everything else… 😉

As with all the good things in life, Pale Red Dot will be intense but short. After all the data is collected (end of March), the hard core analysis will begin and the website will necessarily hibernate for a bit. After that,  results will be sent to a peer review journal and only then an (in)glorious announcement will be made. Who knows what will happen! This process might take several months, but we will do our best to keep you informed as well.

Do you want to know if such a planet exists? So do we! So stay tuned…

…so what kind of articles will you publish?

  • Expert insights and Expert opinions are articles from exoplanet pioneers, leaders of space missions and giant telescope instruments, visionaries and all sorts of rising stars in the field of exoplanet and stellar physics research. Expert opinions will always be released on Sundays (excellent to read with pancakes), while Expert insights will come during week days (really well suited for your daily commute).
  • Observatory life articles will feature how the different observatories work and how modern astronomical observations are obtained. Real life pictures and videos of the action behind-the-scenes included! Observatory life articles will be released every Saturday.
  • Project updates will be released every Friday, and will contain the highlights of the week, including the usual complaints of bad weather. We will not get any data if it gets cloudy, so astronomers are genuinely interested in talking about the weather.

So, are you ready to join our live exoplanet hunt?

If you have questions for us, we’d be happy to answer them on Twitter, @Pale_Red_Dot and #PaleRedDot.

Full resolution video and description available at http://www.eso.org/public/announcements/ann16003/

The search begins Jan 2016

Pale Red Dot is a scientific and outreach project about astronomy and the search of extrasolar planets that will launch on Jan 11th 2016. Pale Red Dot is a joint initiative of the scientists involved in the observations, the outreach office of the European Southern Observatory (www.eso.org), and several supporting institutions including; Queen Mary University of London/UK (www.qmul.ac.uk), Instituto de Astrofísica de Andalucía/Spain ( www.iaa.es), Universidad de Chile (http://www.das.uchile.cl), University of Hertfordshire/UK (www.herts.ac.uk), University of Goettingen/Germany (www.uni-goettingen.de), Université de Montpellier (http://www.lupm.univ-montp2.fr/), LCOGT.net (https://lcogt.net/), and BOOTES telescope network (http://bootes.iaa.es/).

In addition to regular updates on the acquisition of the data, the website will feature contributed articles by world leading researchers, and science writers from several countries. More details on the program and outreach activities will be announced soon.

Stay tuned!