DAWN, STUDYING THE PROTOPLANETS VESTA & CERES

Today, The Grandma has received the wonderful visit of Joseph de Ca'th Lon, one of her best friends. 

 

Joseph loves Astronomy and they have been talking about Dawn, the spacecraft that was launched by NASA on a day like today in 2007.

Dawn is a retired space probe that was launched by NASA in September 2007 with the mission of studying two of the three known protoplanets of the asteroid belt: Vesta and Ceres. 

In the fulfillment of that mission -the ninth in NASA's Discovery Program- Dawn entered orbit around Vesta on July 16, 2011, and completed a 14-month survey mission before leaving for Ceres in late 2012. It entered orbit around Ceres on March 6, 2015. 

In 2017, NASA announced that the planned nine-year mission would be extended until the probe's hydrazine fuel supply was depleted.

On November 1, 2018, NASA announced that Dawn had depleted its hydrazine, and the mission was ended. The spacecraft is currently in a derelict, but stable, orbit around Ceres.

Dawn is 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.

The Dawn mission was managed by NASA's Jet Propulsion Laboratory, with spacecraft components contributed by European partners from Italy, Germany, France, and the Netherlands.

More information: NASA

It was 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 rockets powered by chemical engine, such as the Voyager program, were restricted to flybys.

The first working ion thruster in the US was built by Harold R. Kaufman in 1959 at NASA's Glenn Research Center in Ohio. The thruster was similar to the general design of a gridded electrostatic ion thruster with mercury as its propellant. Suborbital tests of the engine followed during the 1960s, and in 1964 the engine was tested on a suborbital flight aboard the Space Electric Rocket Test 1 (SERT 1). It successfully operated for the planned 31 minutes before falling back to Earth. This test was followed by an orbital test, SERT-2, in 1970.

Deep Space 1 (DS1), which NASA launched in 1998, demonstrated the long-duration use of a xenon-propelled ion thruster on a science mission, and validated a number of technologies, including the NSTAR electrostatic ion thruster, as well as performing a flyby of an asteroid and a comet. In addition to the ion thruster, among the other technologies validated by the DS1 was the Small Deep Space Transponder, which is used on Dawn for long-range communication.

The Dawn mission was designed to study two large bodies in the asteroid belt in order to answer questions about the formation of the Solar System, as well as to test the performance of its ion thrusters in deep space. 

Ceres and Vesta were chosen as two contrasting protoplanets, the first one apparently "wet" and the other "dry", whose accretion was terminated by the formation of Jupiter. The two bodies 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.

More information: NASA-Jet Propulsion Laboratory

The Dawn mission's goal was to characterize the conditions and processes of the Solar System's earliest eon by investigating in detail two of the largest protoplanets remaining intact since their formation.

Although the mission has finished, the data analyses and interpretations will continue for many years. The primary question that the mission addresses is the role of size and water in determining the evolution of the planets.

Ceres and Vesta are highly suitable bodies with which to address this question, as they are two of the most massive of the protoplanets. Ceres is geologically very primitive and icy, while Vesta is evolved and rocky. Their contrasting characteristics are thought to have resulted from them forming in two different regions of the early Solar System.

There are three principal scientific drivers for the mission. First, the Dawn mission can capture the earliest moments in the origin of the Solar System, granting an insight into the conditions under which these objects formed. Second, Dawn determines the nature of the building blocks from which the terrestrial planets formed, improving scientific understanding of this formation. 

Finally, it contrasts the formation and evolution of two small planets that followed very different evolutionary paths, allowing scientists to determine what factors control that evolution.

More information: NASA

 NASA wanted to assure its ability to examine
the spacecraft in orbit for signs of damage.

Marc Garneau

CERES, A DWARF PLANET WITHIN THE ORBIT OF NEPTUNE

Visiting the Astronomical Observatory, Sabadell

Today, The Grandma has travelled to Sabadell, near Barcelona, to visit the Astronomical Observatory. She has been invoted by Joseph de Ca'th Lon, her closest friend, who loves Astronomy and who has explained her the history of Ceres, the largest and first known object in the Asteroid belt discovered by Giuseppe Piazzi on a day like today in 1801.

A new year has started for The Grandma and her friends. A special year for all of them, full of wishes and hopes, especially for The Grandma who is the oldest member of this group. She wants to wish the best for the readers of her blog. Particularly, she wants freedom, peace, respect and democracy for this 2020.

More information: L'Astronòmica de Sabadell

Ceres is the largest object in the main asteroid belt that lies between the orbits of Mars and Jupiter.

With a diameter of 945 km, Ceres is both the largest of the asteroids and the only unambiguous dwarf planet inside Neptune's orbit. It is the 25th-largest body in the Solar System within the orbit of Neptune.

Ceres is the only object in the asteroid belt known to be currently rounded by its own gravity, although detailed analysis was required to exclude Vesta. From Earth, the apparent magnitude of Ceres ranges from 6.7 to 9.3, peaking once at opposition every 15 to 16 months, which is its synodic period. Thus even at its brightest, it is too dim to be seen by the naked eye, except under extremely dark skies.

Ceres was the first asteroid to be discovered by Giuseppe Piazzi at Palermo Astronomical Observatory on 1 January 1801. It was originally considered a planet, but was reclassified as an asteroid in the 1850s after many other objects in similar orbits were discovered.

Ceres appears to be partially differentiated into a muddy (ice-rock) mantle, with a crust that is 60 percent rock and 40 percent ice or less than 30 percent ice. It probably no longer has an internal ocean of liquid water, but there is brine that can flow through the outer mantle and reach the surface. The surface is a mixture of water ice and various hydrated minerals such as carbonates and clay.

Ceres

Cryovolcanoes such as Ahuna Mons form at the rate of about one every fifty million years. In January 2014, emissions of water vapor were detected from several regions of Ceres.

This was unexpected because large bodies in the asteroid belt typically do not emit vapor, a hallmark of comets. Any atmosphere, however, would be the minimal kind known as an exosphere.

The robotic NASA spacecraft Dawn entered orbit around Ceres on 6 March 2015.

Johann Elert Bode, in 1772, first suggested that an undiscovered planet could exist between the orbits of Mars and Jupiter. Kepler had already noticed the gap between Mars and Jupiter in 1596. Bode based his idea on the Titius–Bode law which is a now-discredited hypothesis that was first proposed in 1766. Bode observed that there was a regular pattern in the size of the orbits of known planets, and that the pattern was marred only by the large gap between Mars and Jupiter.

The pattern predicted that the missing planet ought to have an orbit with a radius near 2.8 astronomical units (AU). William Herschel's discovery of Uranus in 1781 near the predicted distance for the next body beyond Saturn increased faith in the law of Titius and Bode, and in 1800, a group headed by Franz Xaver von Zach, editor of the Monatliche Correspondenz, sent requests to twenty-four experienced astronomers, whom he dubbed the celestial police, asking that they combine their efforts and begin a methodical search for the expected planet. Although they did not discover Ceres, they later found several large asteroids.

One of the astronomers selected for the search was Giuseppe Piazzi, a Catholic priest at the Academy of Palermo, Sicily. Before receiving his invitation to join the group, Piazzi discovered Ceres on 1 January 1801. He was searching for the 87th star of the Catalogue of the Zodiacal stars of Mr la Caille, but found that it was preceded by another.

More information: NASA I & II

Instead of a star, Piazzi had found a moving star-like object, which he first thought was a comet. Piazzi observed Ceres a total of 24 times, the final time on 11 February 1801, when illness interrupted his observations. He announced his discovery on 24 January 1801 in letters to only two fellow astronomers, his compatriot Barnaba Oriani of Milan and Johann Elert Bode of Berlin. He reported it as a comet but since its movement is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet. 

In April, Piazzi sent his complete observations to Oriani, Bode, and Jérôme Lalande in Paris. The information was published in the September 1801 issue of the Monatliche Correspondenz.

By this time, the apparent position of Ceres had changed, mostly due to Earth's orbital motion, and was too close to the Sun's glare for other astronomers to confirm Piazzi's observations. Toward the end of the year, Ceres should have been visible again, but after such a long time it was difficult to predict its exact position. To recover Ceres, Carl Friedrich Gauss, then 24 years old, developed an efficient method of orbit determination. 

Giuseppe Piazzi

In only a few weeks, he predicted the path of Ceres and sent his results to von Zach. On 31 December 1801, von Zach and Heinrich W. M. Olbers found Ceres near the predicted position and thus recovered it.

The early observers were only able to calculate the size of Ceres to within an order of magnitude. Herschel underestimated its diameter as 260 km in 1802, whereas in 1811 Johann Hieronymus Schröter overestimated it as 2,613 km.

Piazzi originally suggested the name Cerere Ferdinandea for his discovery, after the goddess Ceres, the Roman goddess of agriculture, Cerere in Italian, who was believed to have originated in Sicily and whose oldest temple was there, and King Ferdinand of Sicily. Ferdinandea, however, was not acceptable to other nations and was dropped. In Modern Greek, it is called Demeter Δήμητρα, after the Greek equivalent of the Roman Cerēs; for the asteroid 1108 Demeter, the classical form of that name Δημήτηρ is used.

The regular adjectival forms of the name are Cererian and Cererean, derived from the Latin genitive Cereris, but Ceresian is occasionally seen for the goddess as in the sickle-shaped Ceresian Lake, as is the shorter form Cerean. The old astronomical symbol of Ceres is a sickle.

Cerium, a rare-earth element discovered in 1803, was named after Ceres. In the same year another element was also initially named after Ceres, but when cerium was named, its discoverer changed the name to palladium, after the second asteroid, 2 Pallas.

More information: In the Sky

The categorization of Ceres has changed more than once and has been the subject of some disagreement. Johann Elert Bode believed Ceres to be the missing planet he had proposed to exist between Mars and Jupiter, at a distance of 419 million km from the Sun. Ceres was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables -along with 2 Pallas, 3 Juno, and 4 Vesta- for half a century.

Ceres follows an orbit between Mars and Jupiter, within the asteroid belt and closer to the orbit of Mars, with a period of 4.6 Earth years. The orbit is moderately inclined and moderately eccentric.

There are indications that Ceres has a tenuous water vapor atmosphere outgassing from water ice on the surface.

Surface water ice is unstable at distances less than 5 AU from the Sun, so it is expected to sublime if it is exposed directly to solar radiation. Water ice can migrate from the deep layers of Ceres to the surface, but escapes in a very short time.

Ceres is a surviving protoplanet, a planetary embryo, that formed 4.56 billion years ago, the only one surviving in the inner Solar System, with the rest either merging to form terrestrial planets or being ejected from the Solar System by Jupiter. However, its composition is not consistent with a formation in the asteroid belt. It seems rather that Ceres formed as a centaur, most likely between the orbits of Jupiter and Saturn, and was scattered into the asteroid belt as Jupiter migrated outward. The discovery of ammonia salts in Occator crater supports an origin in the outer Solar System. However, the presence of ammonia ices can be attributed to impacts by comets, and ammonia salts are more likely to be native to the surface.

Although not as actively discussed as a potential home for microbial extraterrestrial life as Mars, Europa, Enceladus, or Titan, there is evidence that Ceres' icy mantle was once a watery subterranean ocean. The remote detection of organic compounds and the presence of water with 20% carbon by mass in its near surface, could provide conditions favorable to organic chemistry.

More information: Nine Planets

Astronomy teaches the correct use

of the sun and the planets.

Stephen Leacock