{"id":33617,"date":"2022-07-20T00:00:00","date_gmt":"2022-07-20T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=33617"},"modified":"2022-07-21T14:22:29","modified_gmt":"2022-07-21T14:22:29","slug":"from-possible-planets-to-strange-new-worlds","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2022\/07\/20\/from-possible-planets-to-strange-new-worlds\/","title":{"rendered":"From possible planets to strange new worlds"},"content":{"rendered":"\n

With 5,000 exoplanets now confirmed and another 5,000 waiting to follow suit, Ezzy Pearson <\/strong>takes a look at how a deluge of tantalising data is revealing intriguing new worlds every day<\/p>\n\n

\"\"
Exoplanets \u2013 those that orbit stars other than our Sun \u2013 are a rich area of current research <\/figcaption><\/figure><\/div>\n\n

Back in 1992, humanity received its first definitive answer to a question it had been asking for centuries: are there other worlds beyond our Solar System? The answer came in the form of Poltergeist and Phobetor, the first potential planets to have their existence confirmed and become fully fledged exoplanets. <\/p>\n\n

Over the following three decades, dozens of surveys and observation campaigns have tracked down ever more exoplanets in the Milky Way, and on 21 March 2022 the NASA Exoplanet Archive announced it had passed the threshold of 5,000 validated exoplanets.<\/span><\/p>\n\n

But while it took 30 years to reach this number, doubling it will take considerably less time. In the same month as the archive\u2019s announcement, astronomers working on NASA\u2019s Transiting Exoplanet Survey Satellite (TESS) revealed they had obtained another 5,000 exoplanet candidates, which were awaiting confirmation, and there were even more to come.<\/span><\/p>\n\n

\"\"
Tip of the iceberg: the first exoplanet was found circling a pulsar in 1992<\/figcaption><\/figure>\n\n

It\u2019s a huge number to keep track of. Back in the early days when there were only a few known exoplanets, astronomers would each have their own spreadsheets listing them. But as the dozens grew to hundreds and then thousands, it became apparent a dedicated system was needed, leading NASA to create the Exoplanet Archive. <\/p>\n\n

\u201cNASA keeps track of all the planets we\u2019ve found outside our Solar System and anything we know about them,\u201d says Jessie Christiansen, the lead scientist for NASA\u2019s Exoplanet Archive at Caltech, who updates the archive. \u201cIt\u2019s a big database of everything that we know about exoplanets and the stars they orbit.\u201d <\/p>\n\n

I would find 5,000 worlds\u2026 <\/strong><\/h4>\n\n
\"\"<\/figure><\/div>\n\n

With all this information in one place, astronomers can look up any exoplanet they like and discover all its known properties, from size to mass, what kind of star it orbits or if it has any siblings. Or they can sift through the data to find only the exoplanets that match their criteria, such as those with a specific orbit that fits their observing run. Alternatively, they can extract the mass measurements to look at the bulk properties of the entire population of exoplanets discovered so far. In fact, it was doing this that turned up one of the biggest surprises about planetary systems beyond our own. <\/p>\n\n

\u201cOne of the most common sizes of planet is actually in between Earth and Neptune,\u201d says Christiansen. \u201cWe call them super-Earths, or mini-Neptunes depending on exactly where they lie.\u201d <\/p>\n\n

It\u2019s worth bearing in mind when looking at the archive\u2019s planets en masse that they aren\u2019t an accurate reflection of the overall population of exoplanets in our Galaxy, but rather of the ones that are easiest for astronomers to find.<\/span><\/p>\n\n

\u201cAstronomers working on TESS revealed they had obtained another 5,000 exoplanet candidates \u2013 and there were even more to come\u201d <\/p><\/blockquote>\n\n

\"\"
NASA\u2019s Exoplanet Archive (exoplanetarchive.ipac.caltech.edu<\/a>) contained 221 TESS-confirmed planets and 5,767 candidates, at the time of writing <\/figcaption><\/figure>\n\n

\u201cThe missions that have been prolific so far are transit missions,\u201d says Christiansen, referring to the planetary detection method of looking for the brief dip in a star\u2019s brightness as a planet passes in front of it. \u201cThe vast majority of those 5,000 planets are closer to their star than Earth is to the Sun, because we haven\u2019t done a complete job of exploring for all planets, such as we\u2019d find in our Solar System.\u201d <\/p>\n\n

As larger planets create bigger dips and those with shorter orbits transit more frequently, around one third of the planets in the archive are gas giants very close to their star, known as \u2018hot Jupiters\u2019. <\/p>\n\n

\u201cEven though these were the first planets to be found, we actually don\u2019t think they\u2019re very common. <\/p>\n\n

They\u2019re just by far the easiest to find because they\u2019re big and transit so often,\u201d says Christiansen. <\/p>\n\n

Whether super-Earth, mini Neptune or hot Jupiter, the most prolific planet finder of the last 30 years has been the Kepler Space Telescope. It observed a small section of the star-rich Milky Way for almost 10 years and now has over 2,700 confirmed exoplanets in the archive. <\/p>\n\n

And I would find 5,000 more <\/strong><\/h4>\n\n

But what Kepler took a decade to achieve, its successor, TESS, has done in just two years, with 5,000 potential exoplanets already detected and awaiting confirmation. The mission has already completed its primary science phase, spending one year scanning the southern sky and then another scanning the northern sky. Now in its third year, the spacecraft is scanning along the ecliptic. The big difference between exoplanets in the archive and TESS\u2019s \u2018planets\u2019 is that the latter are still only possible planets. So far, only 200 of TESS\u2019s candidates have been verified.<\/span><\/p>\n\n

\"\"
Earth to scale with 55 Cancri e, the first super-Earth found around a main sequence star, where temperatures reach 2,700\u00b0C and a year lasts less than 18 hours <\/figcaption><\/figure>\n\n

\u201cIt takes a lot of work to turn a candidate into a confirmed planet,\u201d says Christiansen. \u201cYou have to get high-resolution imaging to make sure it\u2019s a single star. You need high-resolution spectra to make sure you\u2019ve understood the properties of the star. <\/p>\n\n

There\u2019s a lot of ways it can fail on the way to being a confirmed planet.\u201d <\/p>\n\n

Drawing on their experience with Kepler, the TESS team have put a conservative estimate on their catalogue that around 80 per cent of the candidates will prove to be real and earn a place in the Exoplanet Archive. However, getting these planets their verified place might be difficult, because while Kepler had a portion of its funding dedicated to follow-up, the same is not true for TESS. <\/p>\n\n

\u201cThere\u2019s a much smaller paid component for TESS follow-up,\u201d says Christiansen. \u201cBut there is a much wider community participation because the data is public. We do have an observing programme steering committee, however, with the goal of ensuring we don\u2019t have five teams all working on the same star without knowing it. People are volunteering because the TESS targets are so interesting.\u201d <\/p>\n\n

TESS of the habitables <\/strong><\/h4>\n\n
\"\"
The transit method of detection picks up the dip in brightness of a star as a planet passes between it and the observer <\/figcaption><\/figure>\n\n

Given the interest in these new exoplanets, you might be surprised to hear that TESS\u2019s planets are in many ways similar to those already in the archive. The survey covers each section of sky for just 21 days, during which time a planet needs to transit two or three times to be flagged as a candidate. While there is some overlap between sections, meaning some parts of the sky were observed for as long as six months, most of the planets had orbits of just a few days \u2013 just like with Kepler. Instead, what makes the next 5,000 planets so interesting are the stars they are orbiting. <\/p>\n\n

\u201cKepler did faint stars in one little patch of sky,\u201d says Christiansen. \u201cTESS is looking at bright stars around the whole sky.\u201d Indeed, with so many exoplanets to draw on, researchers are increasingly moving from finding them to learning more about them. One area of keen interest is their atmospheres.<\/span><\/p>\n\n

When a planet transits, some of the starlight passes through the atmosphere. Just like on our own planet, the gases in the air interact with this light \u2013 absorbing some wavelengths, emitting others \u2013 and leave behind a signature, which remains encoded in the light as it travels across lightyears and arrives at Earth. When astronomers observe it, they can decode the signature from the starlight and work out what gases might exist in that planet\u2019s atmosphere. <\/p>\n\n

The brighter the star, the easier this pattern is to see, making TESS\u2019s planets the perfect targets. But even then, a powerful telescope is still needed to pick out the tiny fluctuations caused by the planet. <\/p>\n\n

Fortunately, the recently launched James Webb Space Telescope fits the bill perfectly. <\/p>\n\n

\u201cFor the first time in human history we will be able to collect enough light from a planet as small as Earth to read the composition of its air,\u201d says Lisa Kaltenegger, director of the Carl Sagan Institute and a TESS science team member. The stars that TESS has been finding have all been bright when viewed features editor. Her book <\/span>Robots in Space <\/em>is available through History Press from Earth, but in many cases this is because they are close by, not because they are objectively bright.<\/p>\n\n

\"\"
Three Earth- and Venus-like planets were discovered orbiting an ultracool dwarf star just 40 lightyears away by the TRAPPIST telescope ILLUSTRATION <\/figcaption><\/figure>\n\n

\u201cMost stars in our neighbourhood are actually small, red stars. Eighty per cent of them are smaller than our yellow Sun, actually,\u201d says Kaltenegger. <\/p>\n\n

\u201cThey are not so hot and not so bright.\u201d <\/p>\n\n

As these stars are much cooler than our Sun, so too are the planets around them. In fact, those planets which orbit their star once every 10 days to a month \u2013 acategory many of TESS\u2019s planetary candidates fall into \u2013 would be right in the middle of the star\u2019s habitable zone. <\/p>\n\n

\u201cThis is where it\u2019s not too hot and not too cold, so you could have liquid water on the surface of the planet,\u201d says Kaltenegger. \u201cThat\u2019s one of the key ingredients for life, but also for us to find life on a planet that is far away.\u201d Water will be one of the key chemicals that the JWST will be looking for, but it will be capable of tracking down many more, including carbon dioxide. Here on Earth, the gas is created as a waste product by many forms of life, that then release it out into the atmosphere. If alien life was doing the same on its own planet, JWST would be able to detect it.<\/span><\/p>\n\n

\u201cWe have the first instruments that could actually find signs of life on other worlds,\u201d says Kaltenegger. <\/p>\n\n

\u201cIt\u2019s going to be super hard to do, but it\u2019s possible. If we get really lucky.\u201d <\/p>\n\n

It could just be that the planet which holds the first signs of extrasolar life might have already been discovered and is sitting in the archive, waiting to reveal itself.<\/p>\n\n

<\/div>
\n

The planets of the archive<\/span><\/h4>\n\n\n\n

The new worlds of the Exoplanet Archive are located all over the Milky Way. Here’s where they have been found and what types of planet they are<\/span><\/p>\n\n\n\n

\"\"
Various surveys and detection methods have found exoplanets across the night sky, but some areas have been examined more deeply than others, thus finding more planets. This is particularly obvious in the dense purple patch just left of the galactic centre, which marks the area covered by Kepler. <\/span><\/figcaption><\/figure>\n\n\n\n
\"\"<\/figure><\/div>\n\n\n\n
METHOD USED <\/span><\/h5>\n\n\n\n

\u25cf Radial velocity 913 <\/strong><\/span><\/p>\n\n\n\n

\u25cf Transit 3,846 <\/strong><\/span><\/p>\n\n\n\n

\u25cf Imaging 58 <\/span><\/strong><\/p>\n\n\n\n

\u25cf Microlensing 129 <\/span><\/strong><\/p>\n\n\n\n

\u25cfTiming variations 48 <\/span><\/strong><\/p>\n\n\n\n

\u25cf Orbital brightness modulation 9 <\/span><\/strong><\/p>\n\n\n\n

\u25cf Astrometry 1 <\/span><\/strong><\/p>\n\n\n\n

\u25cf Disc kinematics 1 <\/span><\/strong><\/p>\n\n\n\n

Gas giant: <\/strong><\/span>Planets similar to Jupiter or Saturn, though some are many times larger. Their size means they are some of the easiest to detect.<\/span><\/p>\n\n\n\n

Super-Earth:<\/span><\/strong> Ranging in size from Earth to Neptune, these planets could be rocky like Earth, or shrouded in puffy atmospheres. Despite being numerous elsewhere, they are absent from our own Solar System. <\/p>\n\n\n\n

Neptune-like: <\/span><\/strong>These worlds are similar to the ice giants Neptune and Uranus. Though there have been some examples of \u2018warm Neptunes\u2019 found in orbits closer to their star than the ice giants are to the Sun, they are rarer. <\/p>\n\n\n\n

Terrestrial: <\/span><\/strong>Rocky planets similar to our own home planet. Among the smallest planets known, current methods struggle to detect these worlds. <\/p>\n\n\n\n

<\/p>\n<\/div><\/section>\n\n

<\/div>
\n

What\u2019s next?<\/span><\/h4>\n\n\n\n

A flood of exoplanet detections is expected over the next decade <\/p>\n\n\n\n

\"\"
The Nancy Grace Roman Space Telescope will survey exoplanets in infrared light <\/span><\/figcaption><\/figure>\n\n\n\n

One thing\u2019s for sure: the number of known exoplanets is about to dramatically increase. Not only is TESS continuing to scan the skies for a third year \u2013 and potentially more beyond that \u2013 there are several other missions gearing up to add to the roster as well.<\/span><\/p>\n\n\n\n

The European Space Agency\u2019s Gaia telescope has been monitoring the positions of over a billion stars for several years. Though not its primary goal, these observations could detect upwards of 20,000 planets from the slight wobble caused by their gravitational pull on their star. <\/p>\n\n\n\n

The Nancy Grace Roman Space Telescope is currently being developed by NASA for a launch in 2027. This will use a technique known as microlensing, whereby the telescope looks for starlight being bent by the gravity of unseen masses \u2013 including by exoplanets. Not only will this uncover planets far smaller and further out than the transit method can, it\u2019s expected to unearth some 100,000 of them. \u201cDuring the pandemic we overhauled the archive to accommodate the fact that we\u2019d just got too big for our old tables and our old processes,\u201d says Christiansen. \u201cWe\u2019re looking ahead and realised we need to update our methods to handle the load over the next five years.\u201d<\/span><\/p>\n<\/div><\/section>\n\n

\n\n
\"\"<\/figure><\/div>\n\n

Dr Ezzy Pearson is BBC Sky at Night Magazine\u2019s features editor. Her book Robots in Spac<\/em>e is available through History Press.<\/p>\n\n

photos: NAEBLYS\/ISTOCK\/GETTY IMAGES NASA\/JPL-CALTECH, NASA, NASA\/JPL-CALTECH\/SYSTEM SOUNDS (M. RUSSO AND A. SANTAGUIDA), NASA\/JPL-CALTECH, NASA\/JPL-CALTECH\/R. HURT (SSC), ESA, ESO\/M. KORNMESSER, GSFC\/SVS, ESO<\/p>\n\n

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