![]() In fact, the sunlight that reaches Neptune is 900 times less intense than the sunlight that reaches Earth. Because Neptune is so far from the sun, it receives very little sunlight. Neptune is about 2.8 billion miles (4.5 billion kilometers) from the sun. ![]() Although Neptune is large, it cannot be seen from Earth unless a telescope is used. Neptune’s diameter is about four times greater than Earth’s. This is the length of the planet’s “day.” The rate of rotation of the visible features in Neptune’s atmosphere varies greatly depending on the features’ latitudes. Neptune’s magnetic field rotates once in about 16 hours. It sometimes ventures closer to the sun than Neptune. Of these trans-Neptunian objects, the most familiar is Pluto. Beyond Neptune’s orbit is a region that is traversed by many trans-Neptunian objects. Neptune is the eighth and farthest planet from the sun. In fact, this distance is about 30 times greater than the corresponding value for Earth. Neptune’s average orbital distance from the sun is enormous. (An ellipse is roughly oval-shaped.) The planet travels a huge distance to complete just one orbit. As it revolves, Neptune traces an ellipse. Neptune revolves around the sun once every 165 years. Among the things discovered is that this planet has a thick atmosphere that grows denser with depth, gradually merging with a vast, strange ocean. The probe revealed some remarkable facts about the planet and its moons. Then in 1989 the planetary probe Voyager 2 flew past Neptune. Observations were limited because the planet is so far away. ![]() But very little was known about the planet until recently. Neptune has a rich blue color and is named after the Roman god of the sea. The smallest of the four giant planets in the solar system. The results are published in four papers: 1, 2, 3, and 4.The planet Neptune is the eighth and farthest planet from the sun. “Since the four newly discovered exoplanets are orbiting bright stars, it also makes them targets of prime interest for the mission of the James Webb Space Telescope JWST which might help to solve the riddle of their composition.” “For mini-Neptunes however, density is not enough, and there are still a few hypotheses as to the composition of the planets: they could either be rocky planets with a lot of gas, or planets rich in water and with a very steamy atmosphere,” explained Ulmer-Moll. But it isn’t enough to say for sure what these planets are made up of. Combine these two observations and you can tell the density of a planet, which helps to narrow down its composition. Telescopes like CHEOPS can detect the size of an exoplanet, and ground-based telescopes can detect its mass. However, astronomers are still debating whether they have other compositions like liquid water oceans or a water vapor atmosphere. The planets, named TOI 5678 b, HIP 9618 c, and HD 15906 b and c, have masses between 6 and 20 times that of the Earth, so they could have a thick atmosphere like Neptune and a rocky core like Earth. “This is where CHEOPS comes into play: Focusing on a single star at a time, CHEOPS is a follow-up mission which is perfect to continue observing these stars to find the missing bits of information,” explained fellow researcher Solène Ulmer-Moll. However, to confirm that a planet is definitely present, another telescope needed to observe the host stars for a longer period of time - which CHEOPS was able to do. The first evidence for the presence of the four exoplanets was first provided by NASA’s Transiting Exoplanet Survey Satellite, or TESS, which saw how the brightness of various stars dropped slightly, suggesting the presence of a planet in an event called a transit. In this view the satellite’s telescope cover is open. Artist’s impression of Cheops, ESA’s Characterising Exoplanet Satellite, in orbit above Earth. Mini-Neptunes have relatively cooler surface temperatures of around 300 degrees Celsius. However, hot Jupiters orbit even closer - which gives them very high surface temperatures of over 1,000 degrees Celsius. Mini-Neptunes do orbit close to their stars, typically being found closer to their stars than Mercury is to the sun. They are thought to be very common in our galaxy, but they are hard to spot because they are small and cool compared to the big, bright hot Jupiters which are most commonly detected by exoplanet-hunting telescopes. These planets are notable because they are the “missing link” between rocky Earth-sized planets and ice giants like Neptune. The European Space Agency (ESA)’s CHEOPS satellite has discovered four new exoplanets - and they are a hard-to-detect type called a mini-Neptune.
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