Category: planeta

Saturn and its moons at opposition (The visi…

Saturn and its moons at opposition (The visible moons are (from left to right) Dione, Enceladus, Tethys, Janus, Epimetheus and Mimas

Credit:

NASA, ESA, A. Simon (GSFC) and the OPAL Team, and J. DePasquale (STScI)

Moon, Mercury, Jupiter and Mars Credit: …

Moon, Mercury, Jupiter and Mars

Credit: Mike Salway

This image is a composite of observations ma…

This image is a composite of observations made of Saturn in early 2018 in the optical and of the auroras on Saturn’s north pole region, made in 2017

Credit: ESA/Hubble, NASA, A. Simon (GSFC) and the OPAL Team, J. DePasquale (STScI), L. Lamy (Observatoire de Paris)

Neptune (red arc) completes one orbit around…

Neptune (red arc) completes one orbit around the Sun (center) for every 164.79 orbits of Earth. The light blue object represents Uranus.

Hot Jupiter

Planets in our own solar system have a wide range of properties. They are distinguished by two basic properties, their size and their orbit. The size determines if the planet can have a life-sustaining atmosphere. The orbit affects the surface temperature and whether there could be liquid water on the planet’s surface.

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Hot Jupiters are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital period (P<10 days). The close proximity to their stars and high surface-atmosphere temperatures resulted in the moniker “hot Jupiters”.

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Hot Jupiters are the easiest extrasolar planets to detect via the radial-velocity method, because the oscillations they induce in their parent stars’ motion are relatively large and rapid compared to those of other known types of planets.

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One of the best-known hot Jupiters is 51 Pegasi b. Discovered in 1995, it was the first extrasolar planet found orbiting a Sun-like star. 51 Pegasi b has an orbital period of about 4 days.

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There are two general schools of thought regarding the origin of hot Jupiters: formation at a distance followed by inward migration and in-situ formation at the distances at which they’re currently observed. The prevalent view is migration.

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Migration 

In the migration hypothesis, a hot Jupiter forms beyond the frost line, from rock, ice, and gases via the core accretion method of planetary formation. The planet then migrates inwards to the star where it eventually forms a stable orbit. The planet may have migrated inwar.

In situ

Instead of being gas giants that migrated inward, in an alternate hypothesis the cores of the hot Jupiters began as more common super-Earths which accreted their gas envelopes at their current locations, becoming gas giants in situ. The super-Earths providing the cores in this hypothesis could have formed either in situ or at greater distances and have undergone migration before acquiring their gas envelopes.

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On August 8, 1978, the Pioneer Venus Multiprob…

On August 8, 1978, the Pioneer Venus Multiprobe spacecraft launched to study Venus, a planet that has an atmosphere 100 times denser than Earth’s atmosphere and is hotter than the melting point of zinc and lead. Pioneer Venus Multiprobe was composed of five components: the main spacecraft, the large probe and three identical small probes named North, Day and Night. Built by the Hughes Company in El Segundo, California, and launched on an Atlas-Centaur rocket from Cape Canaveral Air Force Station in Florida, the Pioneer Venus Multiprobe project was managed by NASA’s Ames Research Center in California’s Silicon Valley.

Carrying seven experiments and fitted with a parachute to slow its descent into the atmosphere, the large probe studied the composition of Venus’ atmosphere and clouds. In addition, the large probe measured the distribution of infrared and solar radiation. The three small probes were designed without parachutes, each carrying six experiments. Each probe targeted different parts of Venus. North entered Venus at the high northern latitudes, Night targeted the night side at mid-southern latitudes, and Day targeted the day side at mid-southern latitudes. The main spacecraft carried an additional two experiments designed to study Venus’ upper atmosphere. The five probes collected detailed information about atmospheric composition, circulation and energy balance.

The large probe separated from the main spacecraft 123 days after launch, on November 16, followed by the small probes on November 20, reaching and entering Venus’ atmosphere December 9. While not expected to survive their fiery descent into the dense Venusian atmosphere, all four of the probes transmitted data down to the surface with the Day probe transmitting from the surface for over an hour.

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This image shows the recent observations of …

This image shows the recent observations of the planets Mars and Saturn made with the NASA/ESA Hubble Space Telescope. The observations of both objects were made in June and July 2018 and show the planets close to their opposition.

Credit: NASA/ESA, Hubble

Jupiter and Io taken by the Cassini spacecraft…

Jupiter and Io taken by the Cassini spacecraft on December 1, 2000.

Credit: NASA/JPL/University of Arizona

Jupiter is perpetually covered with clouds com…

Jupiter is perpetually covered with clouds composed of ammonia crystals and possibly ammonium hydrosulfide. The clouds are located in the tropopause and are arranged into bands of different latitudes, known as tropical regions. These are sub-divided into lighter-hued zones and darker belts. The interactions of these conflicting circulation patterns cause storms and turbulence. Wind speeds of 100 m/s (360 km/h) are common in zonal jets. The zones have been observed to vary in width, color and intensity from year to year, but they have remained sufficiently stable for scientists to give them identifying designations.

The cloud layer is only about 50 km (31 mi) deep, and consists of at least two decks of clouds: a thick lower deck and a thin clearer region. There may also be a thin layer of water clouds underlying the ammonia layer. Supporting the idea of water clouds are the flashes of lightning detected in the atmosphere of Jupiter. These electrical discharges can be up to a thousand times as powerful as lightning on Earth. The water clouds are assumed to generate thunderstorms in the same way as terrestrial thunderstorms, driven by the heat rising from the interior.

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Mars Express finds evidence of liquid water un…

A ground-penetrating radar aboard the European Space Agency’s Mars Express satellite has found evidence for a pool of liquid water, a potentially habitable environment, buried under layers of ice and dust at the red planet’s south pole.

“This subsurface anomaly on Mars has radar properties matching water or water-rich sediments,” said Roberto Orosei, principal investigator of the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument, or MARSIS, lead author of a paper in the journal Science describing the discovery.

The conclusion is based on observations of a relatively small area of Mars, but “it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered,” added Orosei.

Scientists have long theorised the presence of subsurface pools under the martian poles where the melting point of water could be decreased due to the weight of overlying layers of ice. The presence of salts in the Martian soil also would act to reduce the melting point and, perhaps, keep water liquid even at sub-freezing temperatures.

Earlier observations by MARSIS were inconclusive, but researchers developed new techniques to improve resolution and accuracy.

“We’d seen hints of interesting subsurface features for years but we couldn’t reproduce the result from orbit to orbit, because the sampling rates and resolution of our data was previously too low,” said Andrea Cicchetti, MARSIS operations manager.

“We had to come up with a new operating mode to bypass some onboard processing and trigger a higher sampling rate and thus improve the resolution of the footprint of our dataset. Now we see things that simply were not possible before.”

MARSIS works by firing penetrating radar beams at the surface of Mars and then measuring the strength of the signals as they are reflected back to the spacecraft.

The data indicating water came from a 200-kilometre-wide (124-mile-wide) area that shows the south polar region features multiple layers of ice and dust down to a depth of about 1.5 kilometres (0.9 miles). A particularly bright reflection below the layered deposits can be seen in a zone measuring about 20 kilometres (12 miles) across.

Orosei’s team interprets the bright reflection as the interface between overlying ice and a pool or pond of liquid water. The pool must be at least several centimetres thick for the MARSIS instrument to detect it.

“The long duration of Mars Express, and the exhausting effort made by the radar team to overcome many analytical challenges, enabled this much-awaited result, demonstrating that the mission and its payload still have a great science potential,” says Dmitri Titov, ESA’s Mars Express project scientist.

The discovery is significant because it raises the possibility, at least, of potentially habitable sub-surface environments.

“Some forms of microbial life are known to thrive in Earth’s subglacial environments, but could underground pockets of salty, sediment-rich liquid water on Mars also provide a suitable habitat, either now or in the past?” ESA asked in a statement. “Whether life has ever existed on Mars remains an open question.”

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