Jupiter’s Irregular Satellites

 

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The planet Jupiter has 67 confirmed moons. This gives it the largest retinue of moons with “reasonably secure” orbits of any planet in the Solar System. In fact, Jupiter and its moons are like a miniature solar system with the inner moons orbiting faster than the others. Eight of Jupiter’s moons are regular satellites, with prograde and nearly circular orbits that are not greatly inclined with respect to Jupiter’s equatorial plane. The remainder of Jupiter’s moons are irregular satellites, whose prograde and retrograde orbits are much farther from Jupiter and have high inclinations and eccentricities. These moons were probably captured by Jupiter from solar orbits. There are 17 recently discovered irregular satellites that have not yet been named.

Image Credit:NASA/ESA/Lowell Observatory/J. Spencer/JHU-APL

Camera That Will Capture More Galaxies


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Construction Starts for Camera That Will Capture More Galaxies Than There Are People on Earth

Beginning in 2022, the most powerful digital camera ever built will start taking pictures of the southern sky. Over the course of a 10-year mission atop a mountain in Chile, the 3.2 gigapixel instrument is expected to accomplish a feat that might be hard to wrap your mind around. It will record tens of billions of galaxies floating in space–the first time a telescope will have ever identified more of the massive celestial objects than there are people on Earth.

Late last month, the U.S. Department of Energy gave its blessing for researchers to start building the camera that will sit at the heart of the Large Synoptic Survey Telescope (LSST). The gif above shows the three-ton, small-car-sized camera on the left. Illustrated is the system that slides filters down in front of the 3.2 gigapixel CCD, which senses light and is a digital camera’s version of film. The filters will let the camera record in light wavelengths from the near-ultraviolet to the near-infrared. Learn more and see images below.

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Two Ribbon Flare

 

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On September 29. 2013, a large magnetic filament erupted on the Sun’s northern hemisphere and produced a C1.2 solar flare. Observation in the EUV showed two elongated ribbon-like structures (hence, the term two-ribbon flare) symmetrically developing on either side of the active region, along the polarity inversion line (neutral line). Two-ribbon flares are extremely powerful eruptions; during magnetic reconnection the magnetic energy is converted into radiation across the electromagnetic spectrumenergetic particles are accelerated up to several hundred MeV or even to GeV range. These high-energy particles are called solar cosmic rays.

Credit & source: LMSAL/Scott Green

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Van Allen Belt & South Atlantic Anomaly

NASA’s first satellite, launched in 1958, discovered two giant swaths of radiation encircling Earth. Five decades later, scientists are still trying to unlock the mysteries of these phenomena known as the Van Allen belt. The belt is named after its discoverer, American astrophysicist James Van Allen.

Space environment is a complex interaction between the planet’s magnetic field, cool plasma moving up from Earth’s ionosphere, and hotter plasma coming in from the solar wind. This dynamic region is populated by charged particles (electrons and ions) which occupy regions known as the plasmasphere and the Van Allen radiation belt. As solar wind and cosmic rays carry fast-moving, highly energized particles past Earth, some of these particles become trapped by the planet’s magnetic field. These particles carry a lot of energy, and it is important to mention their energies when describing the belt, because there are actually two distinct belts; one with energetic electrons forming the outer belt, and a combination of protons and electrons creating the inner belt. The resulting belts, can swell or shrink in size in response to incoming particles from Earth’s upper atmosphere and changes in the solar wind. Recent studies suggest that there is boundary at the inner edge of the outer belt at roughly 7,200 miles in altitude that appears to block the ultrafast electrons from breaching the invisible shield that protects Earth.

Earth’s magnetic field doesn’t exactly line up with the planet’s rotation axis, the belts are actually tilted a bit. Because of this asymmetry, one of the shields that trap potentially harmful particles from space dips down to 200 km (124 mi) altitude.
This dip in the earth’s magnetic field allows charged particles and cosmic rays to reach lower into the atmosphere. Satellites and other low orbiting spacecraft passing through this region of space actually enter the Van Allen radiation belt and are bombarded by protons. Exposure to such radiation can wreak havoc on satellite electronics, and pose serious health risks to astronauts. This peculiar region is called the South Atlantic Anomaly.

Credit: NASA/ESA/M. Kornmesser

Ring System Around Asteroid


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Chariklo is the largest confirmed member of a class of small bodies known as centaurs, which orbit the Sun between Saturn and Uranus in the outer Solar System. A stellar occultation in 2013 revealed that Chariklo has a bright ring system consisting of two narrow and dense bands, separated by a gap of 9 km. 

The existence of a ring system around a minor planet was unexpected because it had been thought that rings could only be stable around much more massive bodies. The origin of the rings is still unknown, but both are likely to be remnants of a debris disk, which could have formed via an impact on Chariklo, a collision with or between one or more pre-existing moons, tidal disruption of a former retrograde moon, or from material released from the surface by cometary activity or rotational disruption. If the rings formed through an impact event with Chariklo, the object must have impacted at a low velocity to prevent ring particles from being ejected beyond Chariklo’s Hill sphere.

Solar wind and Mars’ Atmosphere

Further Reading:

Credit: Chris Smith (HTSI), NASA/Nagoya University

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