Exoplanets

Phosphine is a molecule that consists of one phosphorus and three hydrogen atoms. It is a very toxic gas. The only way phosphine is produced on Earth is by anaerobic bacterias that do not require oxygen for growth. We know that phosphine is common in Jupiter and Saturn's atmospheres and scientists believe that under extreme pressure and temperature this gas can be produced in a non-organic way. Phosphine was discovered in the atmosphere of Venus on 14 September 2020 by the James Clerk Maxwell Telescope JCMT at Mauna Kea Observatory in Hawaii. The result of the study shows that there is a lot of Phosphine in the atmosphere. The UV light from the Sun should destroy the molecules and that suggests that something is producing new Phosphine and that process cannot be explained by chemical reactions. Perhaps there are extreme conditions on Venus that could produce this gas, in a way that we don’t know about yet or it is a sign of life. 

Image credit: NASA/JPL-Caltech

At 50-60 kilometers altitude in Venus' atmosphere, the pressure is the same as Earth and also the temperature. Perfect conditions for airborne bacterial life to thrive and it was just at that altitude the Phosphine gas was discovered. The surface at Venus is about 465°C and the pressure 90 times earth. The interest of sending missions to Venus to search for life has been low before the findings. The focus has been on Mars because the planet's surface has better conditions for that.

 A Japanese space probe Akatsuki has since 2010 been studying the atmosphere of Venus and in a few years, we will get data from Venus upper atmosphere, which could give us an explanation of what is producing Phosphine. 

Several missions to Venus have been conducted in the past. Actually Venus was the first planet that was visited by a space probe in 1962, Mariner 2 flew within 34,400 kilometers of the surface of Venus. Venera was a series of probes developed by the Soviet Union to study Venus. Venera 7 was the first probe to land on Venus in 1970. It sent data to Earth for 23 minutes before it stopped working because of the heat. 

In light of the new findings, NASA said we should prioritize Venus for new missions. The missions that have been proposed before the findings are: 
The Venera-D spacecraft was proposed to Roscosmos in 2003. It would be launched in 2026 or 2031 it would include a lander. NASA is working with Russia on the mission concept.
India's ISRO is developing the Shukrayaan-1 orbiter. It is proposed to be launched in 2023

A new system has been discovered in June 2020. The star known as Gliese 887 or Lacaille 9352  is only located at a distance of about 10.74 light-years from Earth. That makes it the eleventh closest star system to our solar system. The star is a low mass M-type star half the size of our Sun and is the brightest M-type star in the sky. The star is still too faint to see with the naked eye but can be seen with a small telescope. The star has the fourth known highest velocity and is moving at 6.9 arcseconds per year (0.000277778 degrees). The discovery was made by using the HARPS spectrograph at the European Southern Observatory in Chile and HIRES in Hawaii. By using the radial velocity method. 

Image credit: NASA/JPL-Caltech

The system has two confirmed planets both super-earth sized. Gliese 887 b has a mass of 4.2 of Earth and an orbit period of 9 days and Gliese 887 c has a mass of 7.6 of Earth and an orbit period of 22 days. Both planets are closer to the star than the inner edge of the habitable zone. Gliese 887 c has an estimated temperature of 70 degrees celsius. There was a third signal with a period of 50.7 days in the data that suggest that there is a third planet in the habitable zone, but that may be due to stellar activity.

The good news is that the star is a so-called quiet star with not too much stellar activity much lower than our Sun. Which means that the planets will be able to retain their atmosphere. The brightness of the star is almost constant and that would make it easier to detect any atmospheres on the planet. This makes the new system a candidate for more studies for the upcoming James Webb Space telescope.

It is extremely hard to get a direct image of an exoplanet because our instruments are completely blinded by the bright light from the star. For that reason exoplanets are mostly measured by indirect methods like the transit method or radial velocity or gravitational lensing. Direct imaging is the holy grail of exoplanet studies. When astronomers can study exoplanets in detail we can find out information about the planet's atmosphere and composition and even search for biosignature.

One way to solve it is to use an old technique coronagraph invented by the French astronomer Bernard Lyot in 1930 to study the sun's atmosphere. The coronagraph is a telescopic attachment that is designed to block the light from the star.

Some exoplanets have already been directly imaged by blocking the blinding light from the star. An image was taken of the multi-exoplanet system HR 8799 in September 2008. Three planets with masses of ten to seven times Jupiter were observed. The system is young 30 million years and the planets were still glowing from the formation. A fourth planet was discovered around the same system in 2010.

The very first direct image of an exoplanet was already taken in 2004 when a group of astronomers used the VLT telescope to take a picture of a planet (also this planet was several times the size of Jupiter) orbiting a brown dwarf called 2MASS J12073346-3932539 (don't forget the name).

Direct imaging has also been used on Proxima Centauri, our nearest star at 4.25 light-years away. In 2016 an Earth-like planet was discovered in the habitable zone of the system. Measurement by radial velocity in 2019 suggested that the system also has a larger planet Proxima c outside the habitable zone. The image was taken earlier this year by Raffaele Gratton and his colleagues using a VLT telescope and an instrument called SPHERE. The image has some noise and it could be a planet, but the point is brighter than expected. As the planet would not be that large if it exists. One explanation could be that the planet is surrounded by rings like Saturn but with a smaller planet and bigger rings.

One of the most recent news (May 20 2020) is that an image of an exoplanet being born around the star AB Aurigae 520 light-years from Earth has been taken by VLT using SPHERE.

Credit: ESO/Boccaletti et al.

The planet is formatting at the same distance as Neptune from the Sun.

A new Earth-sized exoplanet has been discovered. Kepler-1649 c has a radius of 1.06 times earth. And just like the name suggests the discovery comes from the Kepler data. The Kepler telescope was retired on October 2018 30, 2018.  The planet was originally analyzed by Kepler's Robovetter algorithm. Robovetter is open-source software that automates the process to distinguish between likely planet candidates and false positives in the Kepler dataset.

Image Credit: NASA/Ames Research Center/Daniel Rutter

Robovetter labeled  Kepler-1649 c as a false positive. A computer algorithm could make mistakes when it comes to analyzing tricky signals. Therefore a group of scientists called the Kepler False Positive Working Group has the mission to manually review and confirm all those false positives. They discovered that Kepler-1649 c is not a false positive and published these findings in April 2020.

Earlier in 2017 an earth size planet Kepler-1649 b was discovered around the star the planet orbits closer to the star. The interesting thing is how these two exoplanets are interacting with each other when the first planet makes 4 revolutions around its star the second one makes 9. This makes it a very stable system. Kepler-1649 c is in the habitable zone of its star and could have the same temperature as Earth while Kepler-1649 b could be more similar to Venus. 

The star Kepler-1649 is 300 light-years away and is a red dwarf star with 0.22 times the mass of our sun. The problem with red dwarfs is that they could have a very high stellar activity that gives violent flares, no flares have been observed around Kepler-1649 so far. This is a very interesting discovery that confirms Earth-size planets in the habitable zone are very common around red dwarf stars. And it increases the possibility that one will have the same condition as Earth

Enceladus is the sixth biggest moon of Saturn. The moon that was discovered by William Herschel in 1789 is named after the giant Enceladus of Greek mythology. It won't live up to its name when it comes to size. With a diameter of 500 km, the moon would fit within the north sea. But it will live up to its name when it comes to being one of the strongest candidates for finding non-terrestrial microbial life in our Solar system. Studies have shown half of Earth's biomass lives long under the surface. As microbial life is not just a surface phenomenon the chances of finding this kind of organism outside the so-called goldilocks zone of a star increases. The strongest candidates are moons around gas giants that under their thick icy surface has oceans heated with volcanic activity. One of those candidates is Jupiter's moon Europa that I wrote about in this article. And the other is Enceladus.

Image credit: NASA/JPL-Caltech

On January 16th, 2005 Nasa's probe Cassini's was on a flyby pass Saturn when it captured a very unusual event on Enceladus. There was a bright light coming from the south pole of the moon shining out into space. There were enormous geysers plumbing out vapor into space, more than 8000 times larger than geyser on Earth. Nasa immediately decided that Cassini should have a new mission. To study Enceladus. The probe was reprogrammed from earth to fly into these plumbs and find out was the vapor was made of. It took three years of reprogramming until Cassini was able to do that and the result showed that the vapor was liquid water. Some of the water will fall back on Enceladus as snow but the most will make of the material in Saturn's E ring. The result also showed that the water contains salt which is a very important ingredient for life. The chemicals in the water were very similar to earth and it also showed that something inside Enceladus was heating the water. On June 27, 2018, scientists reported the detection of complex organics compounds from the Cassini data. The Cassini mission ended in September 2017 with the probe crashing into Saturn's atmosphere.

It is very hard getting a probe to investigate Enceladus within a reasonable budget. Several future missions to Enceladus that have been proposed has been canceled. Here is are a list of candidates that are under study and could be our next mission to the icy moon:

• Enceladus Life Finder (ELF) has been twice proposed by Nasa, but it has not been selected yet. The probe would orbit Saturn and fly through the geysers several times.
• Enceladus Life Signatures and Habitability (ELSAH) is another proposed project by Nasa. It has not been selected for launch but has received development funds to improve the instrument. Any details about the mission have not been made public yet.
• Explorer of Enceladus and Titan (E2T) a mission that would investigate both Enceladus and Titan is proposed by ESA in collaboration with NASA. The probe will have high-resolution mass spectrometry to analyze the ice Enceladus.
• Enceladus Explorer (EnEx) is founded by the German Aerospace Center and the research is carried out on seven German universities. EnEx is a lander mission and will be equipped with an iceMole that is a maneuverable ice-melting probe.
• Russian billionaire Yuri Milner, the founder of Breakthrough Initiatives that I wrote about in this article. He is also planning a mission to Enceladus. The low-cost and low mass spacecraft using solar sails will fly through the geysers once and analyze its content for biosignatures. Milner will also receive scientific and technical expertise from Nasa during this project.