Haumea, named after the Hawaiian goddess of fertility, is about a third the mass of Pluto, and has just enough gravity to pull itself into an ellipsoid, or egg shape. It was discovered in by Mike Brown and his team. Eris is the most massive known dwarf planet, and the one that helped turn our definition of a planet upside-down. It even has a moon: Dysnomia.
The founding member of the dwarf family. Want an easy way to remember the eight planets, in order? Just remember this mnemonic: my very excellent mother just served us noodles. For all you currently writing angry tweets to Mike Brown , hold on a sec.
The more we discover about our Universe, the more we realize just how strange and wonderful it is. When Pluto was discovered 80 years ago, we never could have expected the variety of objects in the Solar System.
Categorizing Pluto as a dwarf planet helps us better describe our celestial home. Podcast audio : Download Duration: — 3. Podcast video : Download The requirement that an object clear its orbit to be considered a planet is vague and if applied literally, could exclude all the planets because none has fully cleared its orbital field of nearby asteroids, and Neptune has not cleared its orbit of Pluto. Most of the IAU members who voted on this are not planetary scientists.
No absentee voting was allowed. Also, many planetary scientists are not members of the IAU and therefore had no say in this matter. The four large outer worlds — Jupiter, Saturn, Uranus and Neptune — are sometimes called the Jovian or "Jupiter-like" planets because of their enormous size relative to the terrestrial planets.
They're also mostly made of gases like hydrogen, helium and ammonia rather than of rocky surfaces, although astronomers believe some or all of them may have solid cores. Jupiter and Saturn are sometimes called the gas giants, whereas the more distant Uranus and Neptune have been nicknamed the ice giants.
This is because Uranus and Neptune have more atmospheric water and other ice-forming molecules, such as methane, hydrogen sulfide and phosphene, that crystallize into clouds in the planets' frigid conditions, according to the Planetary Society.
For perspective, methane crystallizes at minus Fahrenheit minus degrees Celsius , according to the U. National Library of Medicine. The IAU defines a true planet as a body that circles the sun without being some other object's satellite; is large enough to be rounded by its own gravity but not so big that it begins to undergo nuclear fusion, like a star ; and has "cleared its neighborhood" of most other orbiting bodies.
Yeah, it's a mouthful. But that restrictive definition helped isolate what should and should not be considered a planet — a problem that arose as astronomers discovered more and more planet-like objects in the solar system.
Pluto was among the bodies that didn't make the cut and was re-classified as a dwarf planet. The problem with Pluto, aside from its small size and offbeat orbit, is that it doesn't clear its neighborhood of debris — it shares its space with lots of other objects in the Kuiper Belt.
Still, the demotion of Pluto remains controversial. The IAU planet definition also put other small, round worlds into the dwarf planet category, including the Kuiper Belt objects Eris , Haumea and Makemake. Ceres , a round object in the Asteroid Belt between Mars and Jupiter, also got the boot.
Ceres was considered a planet when it was discovered in , but it was later deemed to be an asteroid. That still didn't quite fit because it was so much larger and rounder than the other asteroids. Astronomers instead deemed it a dwarf planet in , although some astronomers like to consider Ceres as a 10th planet not to be confused with Nibiru or Planet X. Below is a brief overview of the eight true planets in our solar system , moving from that closest to the sun to farthest from the sun:.
Zipping around the sun in only 88 days, Mercury is the closest planet to the sun, and it's also the smallest, only a little bit larger than Earth's moon. Because its so close to the sun about two-fifths the distance between Earth and the sun , Mercury experiences dramatic changes in its day and night temperatures: Day temperatures can reach a scorching F C , which is hot enough to melt lead.
Meanwhile on the night side, temperatures drop to minus F minus C. Mercury has a very thin atmosphere of oxygen, sodium, hydrogen, helium and potassium and can't break-up incoming meteors, so its surface is pockmarked with craters, just like the moon. Among those findings was the discovery of water ice and frozen organic compounds at Mercury's north pole and that volcanism played a major role in shaping the planet's surface. The second planet from the sun, Venus is Earth's twin in size. Radar images beneath its atmosphere reveal that its surface has various mountains and volcanoes.
But beyond that, the two planets couldn't be more different. Because of its thick, toxic atmosphere that's made of sulfuric acid clouds, Venus is an extreme example of the greenhouse effect. It's scorching-hot, even hotter than Mercury. The average temperature on Venus' surface is F C. At 92 bar, the pressure at the surface would crush and kill you.
And oddly, Venus spins slowly from east to west, the opposite direction of most of the other planets. The Greeks believed Venus was two different objects — one in the morning sky and another in the evening. Because it is often brighter than any other object in the sky, Venus has generated many UFO reports.
The third planet from the sun, Earth is a waterworld, with two-thirds of the planet covered by ocean. It's the only world known to harbor life. This hypothetical planet might be the size of Neptune, and it would have a highly elongated orbit, even more so than Pluto. Planet X would complete one orbit around the Sun once every Some mathematical evidence leads many to believe that this elusive planet indeed exists. In , Caltech astronomers showed that something massive out there disrupts the orbits of at least several other objects located in the Kuiper Belt.
This may indeed be a planet, but further evidence is needed to support this. But let us get back to the known planets of our Solar System. This is the order of the planets. The smallest planet in our Solar System is Mercury, which is only one third the size of Earth, while the biggest planet in the Solar System is Jupiter, which is 11 times bigger than our Earth, and more than 1, could fit inside it if it were hollow.
Mercury is only 0. The farthest planet, Neptune, is 30 AU or 4. Here is a table about the planets in our Solar System, their mass, size, and distance from the Sun. Many other planetary systems have either less, equal, or even more planets than our Solar System. One interesting fact about our Solar System is that it lacks a specific type of planet called a Super-Earth. Super-Earth planets are terrestrial planets that are more massive and much bigger than our Earth, by several times. These giant planets are usually smaller than the gas giants; however, they should harbor life, and it would be interesting to think about how life would evolve on such a planet.
0コメント