The terminology for various objects in the solar system is confusing, especially since many objects, such as Pluto, were initially incorrectly labeled. We can say that the definition of a celestial body often changes because scientists develop better ideas of what things are and how they function.
As we expand our knowledge, we can better define things in the universe. That's why is important to study our solar system and send probes to better investigate unknown environments and worlds.
For example, if the astronomical union didn't decide to introduce the concept of Dwarf Planets, Pluto would still be classified as a normal planet. Sometimes, the nomenclature can make the difference: we would have a solar system with one more planet, and we would be looking for planet ten instead of planet nine!
If you think about it, it is just a matter of names and stuff like that. Or is it?
Ceres and Vesta As Seen From Dawn Mission:
Nowadays the definition of a dwarf planet is based on three main characteristics. The first requirement a body should fulfill to be a dwarf planet is:
1. it must orbit another object.
2. it must have a kind of spherical shape.
This is a consequence of the fact that their mass should be large enough. The more massive an object is, the more likely it will have a spherical shape. Last but not least, a dwarf planet has not cleared its orbit or neighborhood. What does this mean?
This means that they share an orbital space with other similarly-sized celestial bodies and are not Gravitationally Dominant. The most famous example of a dwarf planet is Pluto, which was once considered to be a planet but was redefined.
The definition of an Asteroid is quite different. They are particles of rock and metal that travel through space. Asteroids can be stony or Iron-Nickel, although most asteroids contain both stony and iron-nickel elements.
They can both orbit a planet or travel through the solar system, and usually, they do that in high eccentric orbits. If an asteroid enters the atmosphere of Earth, Mars, Jupiter, or any other planet, it is called a Meteorite. Unlikely dwarf planets, Asteroids are often irregular in shape, because they are too small to have a Spherical Shape.
Today we can make a clear distinction between all kinds of celestial objects, but as we said before, our nomenclature and our definitions of things go along with our knowledge of the universe. And sometimes a mission or a new study can change the way we look at and think about things.
This happened in 2006 when the IAU (International Astronomical Union) decided to introduce the definition of a dwarf planet because we were losing the count of the “planets” - so to speak – of our solar system.
The famous Dawn Mission was the first probe to approach and study a dwarf planet., Ceres. Dawn was a space probe. It left Earth in Sep. 2007 to stud in detail two of the three protoplanets of the Asteroid Belt: Vesta and Ceres.
So, after some years four, to be exact - Dawn entered orbit around Vesta. It was 2011. It chilled and orbit around Vesta collecting data as expected. It was a nice trip, I'm not gonna lie.
It completed a 14-month survey mission before leaving for Ceres in late 2012. Vesta looked really nice. These are some pictures of it. Look how beautiful! (show some pictures)
So smoothly that in 2017 NASA announced that the planned nine-year mission would be extended until the probe's hydrazine fuel supply was depleted. This happened on November 1, 2018, when the Dawn mission depleted its fuel and became a derelict in orbit around Ceres.
This means that if you happen to pass by Ceres, you can still use our fantastic Dawn mission orbiting around the dwarf planet. Dawn was a Guinness world record probe: it was the first spacecraft to orbit two extraterrestrial bodies, the first spacecraft to visit either Vesta or Ceres, and the first to orbit a dwarf planet.
It was also the first NASA exploratory mission to use Ion Propulsion, which enabled it to enter and leave the orbit of two celestial bodies. Previous multi-target missions using conventional drives, such as the Voyager program, were restricted to flybys.
The two bodies studied by Dawn, Ceres, and Vesta, provide a bridge in scientific understanding between the formation of rocky planets and the icy bodies of the Solar System, and under what conditions a rocky planet can hold water.
The second probe to ever visit a dwarf planet was New Horizons, which was launched towards Pluto. Let's see what we know about Ceres and Vesta. Both of them are objects in the asteroid belt.
Ceres alone comprises a third of the total mass of the asteroid belt. This means that, compared to other asteroids in the belt, it is huge! It is not an asteroid, but a dwarf planet. Ceres is named for the Roman goddess of corn and harvests. I'm gonna tell you something: the word cereal comes from the same name.
By studying the spectrum coming from Ceres, astronomers understood that it has a composition similar to that of a Chondrite. A water-rich Carbonaceous one. To understand this a bit more, fragments of meteorites found on earth are often chondrites.
Ceres was called an asteroid for many years, but in 2006 it was finally classified as a dwarf planet. Even though Ceres comprises 25% of the asteroid belt's total mass, Ceres is not that big. Just for comparison, Pluto is still 14 times more massive than Ceres!
Also, this dwarf planet is really interesting because it has water on its surface. Here on Earth, water is essential for life, so it's possible that with this ingredient and a few other conditions met, life possibly could exist there. And hey, stop being that pessimistic!
Even if Ceres does not have living things today, there may be signs it harbored life in the past! Ceres takes 1,682 Earth days, or 4.6 Earth years, to make one trip around the Sun. As Ceres orbits the Sun, it completes one rotation every 9 hours, making its day length one of the shortest in the solar system.
Imagine waking up, going to school, having lunch and dinner, seeing friends...all of this in 9 hours! It would be a nightmare! We think Ceres formed along with the rest of the solar system about 4.5 billion years ago when gravity pulled swirling gas and dust in to become a small dwarf planet.
Scientists say that if Ceres was a bit luckier, it would have become a proper planet. They refer to it as a Planet Embryo, which means it started to form but didn't quite finish. Ceres is more similar to the terrestrial planets (Mercury, Venus, Earth, and Mars) than its asteroid neighborspercentkilometers. It probably has a solid core and a mantle made of water ice.
Certain regions on Ceres' surface couldperiod Ceres could be composed of as much as 25 percent water. If that is correct, Ceres has more water than Earth does! As regards the surface, Ceres is covered in countless small, young craters. However, they are not so big. None of them is larger than 175 miles (280 kilometers) in diameter.
They are craters formed after collisions with the so-called Planetesimals, small rocky bodies in the primordial circumstellar disk from which planets formed. The lack of big craters might be due to layers of ice just below the surface.
The surface features could smooth out over time if ice or another lower-density material, such as salt, is just below the surface. It's also possible that past hydrothermal activity, such as ice volcanoes, erased some large craters.
There are also certain regions on Ceres' surface that could be freeing cold places! These are called “Cold Traps” and they are cold because they are always in shadow. Imagine for example having craters on the surface of a planet or a dwarf planet.
Within some of them, there could be regions that are always in shadow and never see the sun! It's possible that without direct sunlight, these "cold traps" could have water or ice in them for long period. Well, this was pretty much all we knew about Ceres.
But what about Vesta?
First, it is named Vesta after the goddess of the hearth and household in Roman mythology. It holds the record as the second most massive body in the main asteroid belt, and it accounts for almost nine of the total mass of all asteroids.
What the Dawn mission found is that Vesta is that this asteroid is almost spherical, and so is nearly classified as a dwarf planet. It is actually a very peculiar asteroid. Unlike most of them, Vesta has separated into crust, mantle, and core. A Characteristic is called differentiation much like Earth.
The Dawn mission wanted to unveil the secrets of Vesta, and one of these was to understand how and why the differentiation happened. Luckily, we have an answer. The answer is that Vesta formed early, within 1 to 2 million years of the birth of the solar system.
Short-lived radioactive material that was incorporated into bodies that formed during this epoch heated them to the point where the objects melted, allowing the denser materials to sink to the asteroid's core and the lower density materials to rise, in short terms according to Archimede's principle.
Vesta is made of bright materials and dark ones. The bright materials seem to be native rocks, while the dark material is believed to have been deposited by other asteroids crashing into Vesta.
A lot of collisions took place on Vesta during the last 3.5 billion years. Statistical studies from the Dawn mission suggest that about 300 dark asteroids with diameters ranging from one to 10 km (0.6 to six miles) hit Vesta during this period of time.
We know a lot about the interior and the surface of Vesta because it is the source of Howardite, Eucrite and Diogenite. These are strange names given to meteorites found on Earth. They are therefore crucial and provide clues to Vesta's geochemical evolution, a story that was tested and enhanced by the information Dawn provided about the asteroid's surface and interior.
Vesta is believed to have lost about one percent of its mass less than a billion years ago in a massive collision responsible for the Rheasilvia crater, which is about 310 miles (500 kilometers) wide. This 3-D image, called an anaglyph, shows the central complex in Vesta's Rheasilvia impact basin.
To create this anaglyph, two differently colored images are superimposed with an offset to create depth. When viewed through red-blue glasses this anaglyph shows a 3-D view of Vesta's surface.
The images used to generate the two differently colored images that make up this anaglyph were obtained during the approach phase of NASA's Dawn mission in July 2011.
At the time the distance from Dawn to Vesta was about 5,200 kilometers (3,200 miles), which results in an image resolution of about 500 meters (1,600 feet) per pixel.
Vesta was discovered at Bremen, Germany, on Mar. 29, 1807, by Heinrich Wilhelm Olbers, who had previously discovered Pallas.
He proposed incorrectly as it turned out—that Ceres and Pallas were fragments of a destroyed planet, and found Vesta as he searched for more such objects. Vesta was the fourth asteroid ever to be discovered.