Exoplanet-Hunting Satellite CHEOPS Unexpectedly Detects a Strange Planet “Without a Known Equivalent”

Nu2 Lupi Planetary System

This artist’s impression shows the Nu2 Lupi planetary system, which was recently explored by ESA’s exoplanet observer CHEOPS. Credit: ESA

The exoplanet satellite hunter CHEOPS of the European Space Agency (ESA), in which the Instituto de Astrofísica de Canarias (IAC) is participating along with other European institutions, has unexpectedly detected a third planet passing in front of its star while it was exploring two previously known planets around the same star. This transit, according to researchers, will reveal exciting details about a strange planet “without a known equivalent.”

The discovery is one of the first results of CHEOPS (CHaracterising ExOPlanet Satellite) and the first time that an exoplanet has been seen with a period longer than 100 days transiting a star that is sufficiently bright to be seen with the naked eye. The discovery was published in the journal Nature Astronomy.

This bright star similar to the sun, called Nu2 Lupi, is a little more than 50 light-years from Earth, in the constellation of Lupus. In 2019, HARPS (High Accuracy Radial velocity Planet Searcher) of the European Southern Observatory (ESO) in Chile discovered three exoplanets in this system (called b, c, and d) with masses between those of the Earth and Neptune, and with orbital periods of 11.6, 27.6 and 107.6 days respectively. Afterward, NASA’s TESS satellite, designed to detect transiting planets, found that the two interior planets, b and c, transit Nu2 Lupi, making it one of the only three naked-eye stars which have more than one transiting planet.

Nu2 Lupi Planetary System Infographic

This infographic reveals the details of the Nu2 Lupi planetary system, which was recently explored by ESA’s exoplanet watcher Cheops (CHaracterising ExOPlanet Satellite). Credit: ESA, Data: L. Delrez et al (2021)

“Transiting systems such as Nu2 Lupi are of great importance in our understanding of how planets form and evolve, because we can compare several planets around the same bright star in detail,” explains Laetitia Delrez, a researcher at the University of Liege (Belgium) and first author of the article.

“Our idea was to follow up previous studies of Nu2 Lupi and to observe planets b and c passing in front of Nu2 Lupi with CHEOPS, but during a transit of planet c we were amazed to see an unexpected transit of planet d, which is further out within the system,” she adds.

Transits of planets give a valuable opportunity to study their atmospheres, their orbits, their sizes, and their compositions. A transiting planet blocks out a tiny but detectable proportion of the light of its star when it passes in front of it, and it was this tiny drop in the light that led the researchers to their discovery. Because exoplanets with long periods orbit far away from their stars, the possibility of detecting a planet during transit is very small indeed, which makes the finding with CHEOPS a real surprise.

Using the high precision techniques of CHEOPS planet d was found to have some 2.5 times the radius of the Earth, and its orbital period around its star of a little over 107 days, was confirmed. In addition, using archive observations from terrestrial telescopes its mass could be estimated at 8.8 times that of the Earth.

“The amount of radiation from the star which falls onto planet d is quite small compared to many other known exoplanets. If it were in our own solar system Nu2 Lupi d would orbit between Mercury and Venus,” says Mahmoudreza Oshagh, a senior postdoctoral researcher at the IAC, and a co-author of the paper. “Combined with its bright parent star, its long orbital period and its ideal situation for follow-up, this means that planet d is very exciting: it is an exceptional object, with no known equivalent, and it will certainly be a fundamental object for future studies.”

The majority of long period transiting exoplanets discovered until now are orbiting stars that are too faint to allow detailed follow-up observations, which means that we know little about their properties. Nu2 Lupi is, however, sufficiently bright to be an attractive object for other powerful space telescopes such as the NASA/ESA Hubble Space Telescope, the future James Webb Space Telescope, as well as major observatories on the ground. “Given its general properties and its orbit, planet d will be an exceptionally favorable objective to study an exoplanet with a moderate atmospheric temperature around a star similar to the Sun,” adds Laetitia Delrez.

Combining the new data from CHEOPS with archive data from other observatories, the researchers found that planet b is mainly rocky, while planets c and d appear to have large quantities of water surrounded by hydrogen and helium gas. In fact, planets c and d contain much more water than the Earth, a quarter of the mass of each of them is water, in comparison with less than 0.1% on Earth. But this water is not liquid, it is high-pressure ice, or high-temperature water vapor.

“Although none of these planets would be habitable, their diversity makes the system very exciting and a great future perspective to show how these bodies formed and how they have changed with time,” explains Enric Pallé, an IAC researcher and a co-author of the article. “We can also look for rings or moons within the Nu2 Lupi system, because the extreme accuracy and stability of CHEOPS could allow us to detect bodies close to the size of Mars.”

CHEOPS is designed to gather high-precision data of individual stars known to harbor planets, rather than to make a more general survey of possible exoplanets around many stars. This approach and accuracy are proving exceptionally useful in understanding the planetary systems around the stars around us.

“These exciting results show, yet again, the major potential of this satellite,” says Enric Pallé. CHEOPS will not only give us a better understanding of known exoplanets, but as shown by this result and others in the initial phase of the mission, it will enable us to discover new ones, and to reveal their secrets.”

More on this research:

Reference: “Transit detection of the long-period volatile-rich super-Earth ν2 Lupi d with CHEOPS” by Laetitia Delrez, David Ehrenreich, Yann Alibert, Andrea Bonfanti, Luca Borsato, Luca Fossati, Matthew J. Hooton, Sergio Hoyer, Francisco J. Pozuelos, Sébastien Salmon, Sophia Sulis, Thomas G. Wilson, Vardan Adibekyan, Vincent Bourrier, Alexis Brandeker, Sébastien Charnoz, Adrien Deline, Pascal Guterman, Jonas Haldemann, Nathan Hara, Mahmoudreza Oshagh, Sergio G. Sousa, Valérie Van Grootel, Roi Alonso, Guillem Anglada-Escudé, Tamás Bárczy, David Barrado, Susana C. C. Barros, Wolfgang Baumjohann, Mathias Beck, Anja Bekkelien, Willy Benz, Nicolas Billot, Xavier Bonfils, Christopher Broeg, Juan Cabrera, Andrew Collier Cameron, Melvyn B. Davies, Magali Deleuil, Jean-Baptiste Delisle, Olivier D. S. Demangeon, Brice-Olivier Demory, Anders Erikson, Andrea Fortier, Malcolm Fridlund, David Futyan, Davide Gandolfi, Antonio Garcia Muñoz, Michaël Gillon, Manuel Guedel, Kevin Heng, László Kiss, Jacques Laskar, Alain Lecavelier des Etangs, Monika Lendl, Christophe Lovis, Pierre F. L. Maxted, Valerio Nascimbeni, Göran Olofsson, Hugh P. Osborn, Isabella Pagano, Enric Pallé, Giampaolo Piotto, Don Pollacco, Didier Queloz, Heike Rauer, Roberto Ragazzoni, Ignasi Ribas, Nuno C. Santos, Gaetano Scandariato, Damien Ségransan, Attila E. Simon, Alexis M. S. Smith, Manfred Steller, Gyula M. Szabó, Nicolas Thomas, Stéphane Udry and Nicholas A. Walton, 28 June 2021, Nature Astronomy.
DOI: 10.1038/s41550-021-01381-5

10 Comments on "Exoplanet-Hunting Satellite CHEOPS Unexpectedly Detects a Strange Planet “Without a Known Equivalent”"

  1. How is “little more than 50 light years from Earth” the same as the 45.7 light year from earth in the graphic? 🙂

  2. I’ve seen a number of write-ups on CHEOPS and never noticed that the Canary Islands have an Astrophysics Institute.

  3. See, when I hear stuff like three planets having orbital periods of 11.6, 27.6, and 107.6, the fact that they all end with a .6 makes me think that there’s an obvious error or something. I mean how could they all end in .6? I love astronomy, but numbers such as these, or headlines stating “signs of potential life discovered on Venus”, I take EVERYTHING in those articles with more than a few hefty grains of “skeptical salt”.

  4. Not sure I understand the significance of a “naked eye” star.

  5. Concerning probabilities | August 29, 2021 at 2:18 am | Reply

    Someone was worrying about the repeated .6; while I would never tell someone to accept data blindly, remember that:
    (a) those numbers are at the center of confidence intervals, so the true values are likely near to but not exactly the reported values
    (b) if we assume that the true values are “random,” the likelihood of seeing the same value three times (or, equivalently, of the second and third planet having the same digit in the “tenths” place) is 1/100 – uncommon, but not at all requiring a “suspension of disbelief”

  6. As our observational technologies evolve we are more able to detect and determine the characteristics of exo planets, a very exciting time for astrophysics. The reality is to get to these planetary systems we require a not now known type of propulsion.

  7. There is no planet b

  8. Michael A Michalski | September 1, 2021 at 8:50 am | Reply

    Its 11.6 days, 27.6 days and 107.2 days NOT 107.6 days. So two of the three numbers happen to round to the same last digit. We can list the possible ways at least two of the last digits are the same. (XXY),(XYX),(YXX),(XXX). Since there are 10 different possible digits, there are 40 possible ways that at least two of the last digit could be the same. There are 1000 possible combinations of last digits. (10^3). The probability of something happening is the number of ways it can happen divided by the total number of possibilities. So we have 40/1000. The probability of at least two of those numbers having the same last two digits is therefore 1 in 25. So you should expect this to be a somewhat common event. Similarly the probability of 3 identical trailing digits is 1 in 100. Again, not particularly shocking.

    There is however a grain of truth in the skepticism about data values that look “funny”. While a single set of data can’t tell you whether something is fraudulent, it’s a valid technique to look at a large set of data and perform a statistical analysis on the numbers.It turns out that, in part for exactly the concerns stated, a person creating fraudulent data will end up missing the numbers away from the truly random. It makes sense. If your going to write down four fraudulent numbers, your probably not going to write down numbers that are identical, or all end in the same number or are multiples of each other, etc. However, these things are expected to occur with a predictable frequency in real data. So if ask you to take four measurements of something, say the temperature in your refrigerator, every day for 3 years, and you just right down four “random” numbers every day, they probably are NOT really random. You won’t choose sets of numbers like 27.5,27.5,27.5,27.5 or 28.6,27.6,26.6,25.6. they look odd and non random. But we expect those obviously visible patterns to occur with predictable frequency. Now, if the days is random, then just as something MIGHT happen, it might not. We can calculate the chances of that not happening as well.

    For example, I have you test a pair of blood glucose meters on a standard test solution 1000 times. After 10 measurements you get bored and decide to be “clever” You look at the the measurements, get an idea of the spread and write down 990 more numbers that are in that range but vary “randomly” around the average. But I suspicious. You see kinda shady and I noticed you spent a lot of time on the internet looking at adult entertainment. So I look deeper.

    There are 10 ways that a pair of measurements might have the same last digit. There are 100 different combinations of two of those digits. That means we expect to see the same last digit about 1 out of 10 times. I noticed that happened only once, in the first 10 pairs, and then never again. The chance of it happening is 1 out of 10. So the chance of it not happening is 9 out of 10. The chance of it not happening 990 times in a row, is (0.9)^990. That is about 5×10^-42. Thats a vanishingly small probability. Its like picking the winning lottery numbers every day for a week.

  9. Habitat is good for humanity. Until we are capable of traveling to distances we can see in a reasonable time. It’s still just that. A dream , there might be life elsewhere in this universe. Seems there’s two things that need improvement. Telescopes andengines to get us there.

  10. Blah blah, blah blah blah…blah

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