My Science School

In 1801, while making a star map, Giuseppe Piazzi accidentally discovered a small object 1000 kilometers (600 miles) in diameter between the orbits of Mars and Jupiter. Piazzi named the object Ceres. It was the first asteroid to be discovered. In 1802, two more were discovered. Asteroids are numbered in order of their discovery and many have been named. For example, the first asteroid discovered is 1 Ceres, the second is 2 Pallas, etc. More than 400,000 asteroids have been discovered in the main asteroid belt.

In August, 2006, the International Astronomical Union passed a resolution redefining how celestial bodies are classified. Under this new classification system, Ceres is designated a dwarf planet because it orbits the Sun, has enough mass to form in a spherical shape, has not cleared the area around its orbit, and is not a satellite.

In 1801, while making a star map, Italian priest and astronomer Giuseppe Piazzi accidentally discovered the first and largest asteroid, Ceres, orbiting between Mars and Jupiter. Although Ceres is classified today as a dwarf planet, it accounts for a quarter of all the mass of all the known asteroids in or near the main asteroid belt.

Since about 2000, NASA has spearheaded a campaign to identify and track near-Earth asteroids. Programs like the Catalina Sky Survey in Arizona and the Pan-STARRS telescopes in Hawaii specialize in identifying these objects and have each discovered thousands of asteroids, according to CNEOS.

Asteroids are leftovers from the formation of our solar system about 4.6 billion years ago. Early on, the birth of Jupiter prevented any planetary bodies from forming in the gap between Mars and Jupiter, causing the small objects that were there to collide with each other and fragment into the asteroids seen today. 

Understanding of how the solar system evolved is constantly expanding. Two fairly recent theories, the Nice model and the Grand Tack, suggest that the gas giants moved around before settling into their modern orbits. This movement could have sent asteroids from the main belt raining down on the terrestrial planets, emptying and refilling the original belt.

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Yes, asteroids can have moons! Some of the larger asteroids in our Solar System actually do have moons. In 1993, a tiny moon called Dactyl was discovered orbiting the large asteroid Ida. Dactyl is only about 1 mile wide, while Ida is about 19 miles across. Since then, several other moons have been discovered orbiting asteroids. In 1999, an 8 mile wide moon called Petit-Prince was discovered orbiting the 135 mile wide asteroid Eugenia. In 2000, the 90 mile wide asteroid Pulcova was discovered to have its own moon, about nine miles wide. Over two dozen more have been discovered.

The first asteroid moon was discovered in pictures that were snapped 25 years ago today. The Galileo spacecraft was passing through the asteroid belt on its way to Jupiter. It flew close to Ida, an asteroid that’s about 35 miles long. When mission scientists looked at the pictures of Ida a few days later, they discovered a mile-wide companion. They named it Dactyl, after creatures from Greek mythology that lived on Mount Ida.

The most likely way for an asteroid to get a moon is through a collision with another asteroid. If the impact is at the right speed and angle, it can chip off a chunk of rock and send it into orbit. If the impact is too strong, though, the debris sails away into space, leaving the parent asteroid behind.

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The largest asteroid is called Ceres. It is about one-quarter the size of the moon and orbits the sun between Mars and Jupiter in a region called the asteroid belt. Unlike most asteroids, Ceres is spherical in shape. Ceres was discovered by the Italian astronomer Giuseppe Piazzi in 1801 as he searched for a planet which was predicted to exist between Mars and Jupiter. It was the first asteroid ever discovered. It is a dwarf planet.

Ceres was designated a dwarf planet, a new category of solar system objects defined in August 2006 by the International Astronomical Union. (For a discussion of that decision, see planet.) The U.S. space probe Dawn studied the dwarf planet from March 2015 to November 2018. Dawn observed two very bright spots, Cerealia Facula and Vinalia Faculae, in Occator crater on Ceres. The bright spots are highly reflective salts left behind when briny water from an underground reservoir percolated upward and evaporated. The water percolated through fractures left behind when the crater formed 20 million years ago. The salty regions have not been darkened by micrometeorite impacts, indicating that the bright spots formed in the last 2 million years. Because the bright spots contain salt compounds with water that has not dehydrated, the briny water must have percolated upward in the last few hundred years, suggesting that the salty liquid water underneath the crater has not frozen and is perhaps currently percolating from underground.

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Scattered in orbits around the sun are bits and pieces of rock left over from the dawn of the solar system. Most of these objects, called planetoids or asteroids — meaning "star-like" — orbit between Mars and Jupiter in a grouping known as the Main Asteroid Belt.

The Main Asteroid Belt lies more than two-and-a-half times as far as Earth does from the sun. It contains millions of asteroids, according to NASA. Most of these are relatively small, from the size of boulders to a few thousand feet in diameter. But some are significantly larger.

The Main Belt lies between Mars and Jupiter, roughly two to four times the Earth-sun distance, and spans a region about 140 million miles across. Objects in the belt are divided into eight subgroups named after the main asteroids in each group. These groups are the Hungarias, Floras, Phocaea, Koronis, Eos, Themis, Cybeles and Hildas.

Although Hollywood often displays ships making close calls through asteroid belts, the trip is generally uneventful. A number of spacecraft have safely traveled through the asteroid belt without incident, including NASA's New Horizons mission to Pluto.

"Fortunately, the asteroid belt is so huge that, despite its large population of small bodies, the chance of running into one is almost vanishingly small — far less than one in a billion," wrote New Horizons principle investigator Alan Stern. "If you want to come close enough to an asteroid to make detailed studies of it, you have to aim for one."

Within in the asteroid belt are relatively empty regions known as Kirkwood gaps. These gaps correspond to orbital resonances with Jupiter. The gas giant's gravitational pull keeps these regions far emptier than the rest of the belt. In other resonances, the asteroids can be more concentrated.

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Near-Earth objects (NEO) are asteroids, comets and large meteoroids whose orbit intersects Earth's orbit and which may therefore pose a collision danger.

Due to their size and proximity, NEOs are also more easily accessible for spacecraft from Earth and are important for future scientific investigation and commercial development.

In fact, some near-Earth asteroids can be reached with a much smaller change in velocity than the Moon.

In the United States, NASA has a congressional mandate to catalogue all NEOs that are at least 1 kilometer (0.6 miles) wide.

At this size and larger, an impacting NEO would cause catastrophic local damage and significant to severe global consequences.

Approximately 800 of these NEOs have been detected.

According to the most widely accepted estimates, there are still 200 more that have not been found yet.

The United States, European Union and other nations are currently scanning for NEOs in an effort called Spaceguard.

Currently efforts are under way to use an existing telescope in Australia to cover the approximately 30 percent of the sky that is not currently surveyed.

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Pluto has five moons: Charon, Styx, Nix, Kerberos, and Hyrda. Charon is the largest of Pluto's moons and was discovered by US astronomer James Christy on June 22, 1978, roughly fifty years after the dwarf planet's discovery. Two more moons, Nix and Hydra, were identified on May 15, 2005, by members of the Pluto Companion Search Team while preparing for the New Horizons mission. Kerberos was first identified on July 20, 2011, while Styx was discovered on July 7, 2012.

Charon, which is Pluto’s innermost and biggest moon, is approximately 597 miles from the surface of Pluto and is nearly half its size. The moon is primarily gray, but its northern pole has a reddish tint. A large percentage of Charon's surface is covered by ice, but the reddish part of its north pole is composed of tholins, which are ethane, methane, or carbon dioxide molecules that are sometimes mixed with nitrogen or water. Charon’s northern pole is reddened by continuous exposure to ultraviolet light from the Sun. Charon orbits Pluto every 6.3 days, and the two planetary bodies are gravitationally locked, meaning the same face is maintained during orbit. Although the surface of Charon appears icy and rigid, more than 50% of its interior is composed of rock. Pluto and Charon have their barycenter about 600 miles above Pluto's surface. 

Hydra, Nix, Kerberos, and Styx are 34 miles, 26 miles, 7 miles, and 4 miles wide along their longest axis, respectively. These moons are smaller than Charon and irregularly shaped, and rotate at two to four times the distance of Charon, ranging from 26,532 miles (Styx) to 40,264 miles (Hydra). Styx has an elongated shape, and Nix is an oddly shaped celestial body. Hydra has an uneven surface that includes some craters, and it measures roughly 34 miles by 25 miles. Hydra orbits Pluto every 39 days, while Nix orbits the dwarf planet every 25 days. Kerberos has the most mysterious appearance, as its surface appears lumpy. It takes Kerberos 32 days to orbit Pluto, and it orbits between Hydra and Nix, exerting a strong gravitational pull on the other moons despite its small size.

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The inner edge of the Kuiper Belt begins at the orbit of Neptune, at about 30 AU from the Sun. (1 AU, or astronomical unit, is the distance from Earth to the Sun.)

The inner, main region of the Kuiper Belt ends around 50 AU from the Sun. Overlapping the outer edge of the main part of the Kuiper Belt is a second region called the scattered disk, which continues outward to nearly 1,000 AU, with some bodies on orbits that go even farther beyond.

Astronomers think the icy objects of the Kuiper Belt are remnants left over from the formation of the solar system. Similar to the relationship between the main asteroid belt and Jupiter, it's a region of objects that might have come together to form a planet had Neptune not been there. Instead, Neptune's gravity stirred up this region of space so much that the small, icy objects there weren't able to coalesce into a large planet.

Just outside of Neptune’s orbit is a ring of icy bodies. We call it the Kuiper Belt.

This is where you’ll find dwarf planet Pluto. It’s the most famous of the objects floating in the Kuiper Belt, which are also called Kuiper Belt Objects, or KBOs.

There are bits of rock and ice, comets and dwarf planets in the Kuiper Belt. Besides Pluto and a bunch of comets, other interesting Kuiper Belt Objects are Eris, Makemake and Haumea. They are dwarf planets like Pluto.

Credit : NASA Solar System Exploration

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It takes 248 Earth years for Pluto to complete one orbit around the Sun. Its orbital path doesn't lie in the same plane as the eight planets, but is inclined at an angle of 17°. Its orbit is also more oval-shaped, or elliptical, than those of the planets. That means that sometimes Pluto is a lot nearer to the Sun than at other times, At times Pluto's orbit brings it closer to the Sun than Neptune. The last time this happened was from 1979 to 1999. It won't happen again until 2227.

Like the planet Uranus, Pluto rotates on its side, its axis tilted about 120 degrees.

As Pluto moves closer to the Sun, ices on its surface warm slightly and sublime ("evaporate" from solid to gas) to form a thin, mostly nitrogen atmosphere. As it moves away from the Sun, the gases cool and refreeze. The atmosphere may vanish as Pluto moves farther from the Sun.

Many Hubble Space Telescope images were combined to create these views of Pluto's surface. Distinct geologic features can't be seen, but the colors may indicate different surface compositions. When compared with earlier observations, these images suggest Pluto's face may change through time, perhaps due to seasonal changes in surface ices.

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When Pluto was reclassified in 2006 from a planet to a dwarf planet, there was widespread outrage on behalf of the demoted planet. As the textbooks were updated, the internet spawned memes with Pluto going through a range of emotions, from anger to loneliness. But since the release of New Horizons images showing a very prominent heart-shaped feature on the surface, the sad Pluto meme has given way to a very content, loving Pluto that would like to once again be visited by a spacecraft.

The Disney cartoon character Pluto, Mickey's faithful dog, made his debut in 1930, the same year Tombaugh discovered the dwarf planet. There is speculation that Walt Disney named the animated dog after the recently discovered planet to capitalize on its popularity, but other accounts are less certain of a direct link. 

Pluto is a dwarf planet that lies in the Kuiper Belt, an area full of icy bodies and other dwarf planets out past Neptune. Pluto is very small, only about half the width of the United States and its biggest moon Charon is about half the size of Pluto.

Almost all the planets travel around the Sun in nearly perfect circles. But not Pluto. It takes an oval-shaped path with the Sun nowhere near its center. What's more, its path is quite tilted compared to the planets.

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On Jupiter, a storm's been brewing for more than 300 years. Known as the Great Red Spot, this swirling high-pressure region is clearly visible from space, spanning a region in Jupiter's atmosphere more than 10,000 miles (16,000 kilometers) wide — about one and a quarter times the diameter of Earth.

But there's even more to the churning tempest than meets the eye; according to two new studies published Oct. 28 in the journal Science, Jupiter's Great Red Spot is also extraordinarily deep, extending as many as 300 miles (480 km) into the planet's atmosphere — or about 40 times as deep as the Mariana Trench on Earth.

That's far deeper than researchers expected, with the bottom of the storm extending well below the atmospheric level where water and ammonia are expected to condense into clouds, the researchers wrote. The storm's deep roots suggest that some as-yet unknown processes link Jupiter's interior and deep atmosphere, driving intense meteorological events over much larger scales than previously thought, the researchers said.

"We're getting our first real understanding of how Jupiter's beautiful and violent atmosphere works," Scott Bolton, principal investigator of NASA's Juno Mission and lead author of one of the new papers, said in a statement.

Both new studies relied on observations from NASA's Juno probe, which entered Jupiter's orbit in 2016 and has since completed 36 passes of the nearly 87,000-mile-wide (140,000 km) gas giant. In one study, scientists examined the Great Red Spot using the probe's microwave radiometer — a tool that detects microwaves emitted from inside the planet. Unlike the radio and infrared radiation emitted by the gas giant, microwaves can make it all the way through the planet's thick cloud layer, according to NASA.

By studying the microwave emissions that made it through the Great Red Spot, the authors of the first study determined that the storm extends more than 200 miles, or around 350 km, deep.

The second study found the spot may be even bigger than that. That paper's authors examined the Great Red Spot using Juno's gravity detection tools. Synthesizing data from 12 flights that passed by the spot — including two direct overhead flights — the researchers calculated where the storm was concentrating the most atmospheric mass over the planet, allowing them to estimate its depth. The authors determined that the spot reaches a maximum depth of about 300 miles (500 kilometers) below the cloud tops.

As deep as this seems, the Great Red Spot is still much shallower than the enormous jets of wind that surround and power it, the researchers said; those bands of wind extend to depths of about 2,000 miles (3,200 km) below the cloud tops. The reasons for this discrepancy remain a puzzle, but the spot's relative shallowness might be due to another recently-discovered phenomenon: The Great Red Spot is shrinking, the researchers said, having lost about a third of its width since 1979.

The future of the spot remains uncertain, but whatever happens, Juno will continue to keep tabs on our big, gassy neighbor in space.

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It is the largest planet in the solar system, but just how big is Jupiter? The gas giant is approximately 318 times as massive as Earth, according to planetary scientist Alan Boss. If the mass of all of the other planets in the solar system were combined into one "super planet," Jupiter would still be two and a half times as large.

Jupiter has a mean radius of 43,440.7 miles (69,911 kilometers), according to NASA Science. That's about a tenth that of the sun. However, its rapid rotation — it spins once every 9.8 hours, according to the journal Acta Astronautica — causes it to bulge at the equator, where the diameter is 88,846 miles (142,984 km). In contrast, the diameter at the poles is only 83,082 miles (133,708 km). This stretched shape is known as an oblate spheroid.

According to NASA's statistics, if you were to walk around the equator of Jupiter, you would travel 272,946 miles (439,264 km), over 10 times the distance around Earth's center line.

Because Jupiter is made of gas, mostly, its surface is considered uniform. As such, it lacks high and low points — mountains and valleys — such as those found on rocky terrestrial planets.

Jupiter's structure resembles that of the sun, but would need to be 75 times its present mass to undergo the fusion of hydrogen that fuels a star, according to the journal Science. The mass of the largest gas giant planets found outside of the solar system is often given in terms of the enormous planet.

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The beauty of Saturn’s rings have resulted in the planet being nicknamed the Jewel of the Solar System. However, all of the gas giants have systems of rings around them, including the king of the planets, Jupiter.

• Halo — This is a faint, wide doughnut-shaped ring, and the closest to Jupiter.
• The Main ring — Extending out of the halo ring is the Main ring. The two small moons Adrastea and Metis orbit here within the main ring and are thought to be the source of dust of this ring.
• Gossamer rings — These are very faint and wide composed of microscopic debris from the moons Amalthea and Thebe. The Gossamer rings extend beyond the orbit of the moon Amalthea.

It is not entirely clear how ring systems form in general. Jupiter’s faint rings are likely from meteor bombardment of its moons, sending material into space. However, other stronger ring systems have numerous plausible origins. It’s possible they come from material leftover from the formation of our solar system, captured by the planets. Alternatively they could be broken up pieces of the gas giant’s moons, perhaps resulting from a catastrophic collision or being torn apart by the gravity of the planet itself.

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Earth only has one moon, but dozens of natural satellites revolve around Jupiter, the biggest planet in our solar system. And new members in the Jupiter posse are still being discovered. On July 16, 2018, it was announced that a team of astronomers had found 12 previously unknown moons around the planet.

In 1610, the great astronomer Galileo Galilei noticed four heavenly bodies that appeared to revolve around Jupiter. Named Io, Europa, Ganymede and Callisto, these are Jupiter's biggest moons by far — and they were the first to be discovered. As stargazing technology grew more sophisticated, it became clear that the quartet had lots of company. Sheppard's team just brought the total number of identified Jovian moons (i.e. moons which revolve around Jupiter) up to 79.

Jupiter had always had the most moons in the solar system, until the summer of 2019. That's when astronomers discovered that Saturn had another 20 moons, bringing its total to 82. Uranus boasts 27 and Neptune has 14. Mars, our beloved next-door neighbor, possesses two satellites: Deimos and Phobos. And if that's making you feel insecure about Earth's lonely moon, at least you can take solace in the fact that Mercury and Venus are totally moon-less.

There's a reason why Jupiter has so many satellites while other planets — ours, for instance — have so few. It all comes down to gravity.

Astronomers divide the planets within our solar system into two categories. Mercury, Venus, Earth, and Mars are the so-called "terrestrial" or "inner" planets while Jupiter, Saturn, Uranus, and Neptune have been classified as "gas giants," also known as "outer planets."

The size gap between those factions is quite considerable; Although Uranus is the smallest outer planet, it's still 15 times more massive than Earth, the largest of the inner planets. None of the other planets can compete with Jupiter in terms of sheer bulk, however. You'd need more than 300 duplicates of our puny home world to equal Jupiter's colossal mass. It's an absolute monster.

Now, as Isaac Newton observed, there's a positive correlation between the mass of an object and the strength of its gravitational field. Because the gas giants are so massive, they're able to attract more satellites.

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The brilliant planet Jupiter dazzles anyone with a clear sky. Roman observers named Jupiter after the patron deity of the Roman state following Greek mythology, which associated it with the supreme god, Zeus. But when Galileo turned his telescope skyward in 1610, Jupiter took on new significance. Galileo discovered the planet’s four principal moons — and witnessed the first clear observation of celestial motions centered on a body other than Earth. 

Astronomers recognized Jupiter as the largest planet in the solar system long before any spacecraft provided detailed exploration. The planet’s mammoth size — 88,846 miles (142,984 kilometers) at the equator — holds 2.5 times the mass of all the other planets combined. This makes Jupiter the most dominant body in the solar system after the Sun. The planet’s volume is so great that 1,321 Earths could fit inside it.

Jupiter’s size and compositional similarity to brown dwarfs and small stars have led some to label it a “failed star.” Had the planet formed with more mass, they claim, Jupiter would have ignited nuclear fusion and the solar system would have been a double-star system. Life might never have evolved on Earth because the temperature would have been too high and its atmospheric characteristics all wrong.

But although Jupiter is large as planets go, it would need to be about 75 times its current mass to ignite nuclear fusion in its core and become a star. Astronomers have found other stars orbited by planets with masses far greater than Jupiter's.

What about substellar brown dwarfs? Our largest planet still doesn’t come close to these “almost stars.” Astronomers define brown dwarfs as bodies with at least 13 times Jupiter’s mass. At this point, a hydrogen isotope called deuterium can undergo fusion early in a brown dwarf’s life.

So, while Jupiter is a planetary giant, its mass falls far short of the mark for considering it a failed star.

Credit : Astronomy 

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