Orbits of Potentially Hazardous Asteroids

Are asteroids dangerous? Some are, but the likelihood of a dangerous asteroid striking the Earth during any given year is low. Because some past mass extinction events have been linked to asteroid impacts, however, humanity has made it a priority to find and catalog those asteroids that may one day affect life on Earth. Pictured here are the orbits of the over 1,000 known Potentially Hazardous Asteroids (PHAs). These documented tumbling boulders of rock and ice are over 140 meters across and will pass within 7.5 million kilometers of Earth — about 20 times the distance to the Moon. Although none of them will strike the Earth in the next 100 years — not all PHAs have been discovered, and past 100 years, many orbits become hard to predict. Were an asteroid of this size to impact the Earth, it could raise dangerous tsunamis, for example. To investigate Earth-saving strategies, NASA’s Double Asteroid Redirection Test (DART) is planned for launch later this year. Of course rocks and ice bits of much smaller size strike the Earth every day, usually pose no danger, and sometimes creating memorable fireball and meteor displays. via NASA https://ift.tt/2XX0n64

Mars Rock Rochette

Taken on mission sol 180 (August 22) this sharp image from a Hazard Camera on the Perseverance rover looks out across a rock strewn floor of Jezero crater on Mars. At 52.5 centimeters (21 inches) in diameter, one of the rover’s steerable front wheels is at lower left in the frame. Near center is a large rock nicknamed Rochette. Mission planners don’t want to avoid Rochette though. Instead Perseverance will be instructed to reach out with its 2 meter long robotic arm and abrade the rock’s surface, to determine whether it has a consistency suitable for obtaining a sample, slightly thicker than a pencil, using the rover’s coring bit. Samples collected by Perseverance would be returned to Earth by a future Mars mission. via NASA https://ift.tt/3ztb8Lw

Elephant s Trunk and Caravan

Like an illustration in a galactic Just So Story, the Elephant’s Trunk Nebula winds through the emission nebula and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Also known as vdB 142, seen on the left the cosmic elephant’s trunk is over 20 light-years long. Removed by digital processing, no visible stars are in this detailed telescopic close-up view highlighting the bright swept-back ridges that outline pockets of cool interstellar dust and gas. But the dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning over 5 degrees. This starless rendition spans a 1 degree wide field of view though, about the angular size of 2 full moons. Of course the dark shapes below and right, marching toward the winding Elephant’s Trunk, are known to some as The Caravan. via NASA https://ift.tt/2Y5I8vz

A Blue Hour Full Moon

Nature photographers and other fans of planet Earth always look forward to the blue hour. That’s the transition in twilight, just before sunrise or after sunset, when the Sun is below the horizon but land and sky are still suffused with a beautiful blue light. After sunset on August 21, this blue hour snapshot captured the nearly full Moon as it rose opposite the Sun, above the rugged Italian Alps from Cortina d’Ampezzo, Italy. Sharing bluish hues with the sky, the rocky pyramid of Monte Antelao, also known as the King of the Dolomites, is the region’s prominent alpine peak. The moonlight is yellow, but even so this full Moon was known to some as a seasonal Blue Moon. That’s because by one definition the third full Moon of a season with four full moons in it is called a Blue Moon. Recognizing a season as the time between a solstice and an equinox, this season’s fourth full Moon will be rising in the blue hour of September 20, just before September’s equinox. via NASA https://ift.tt/2WqrfdQ

Solar System Ball Drop

Does a ball drop faster on Earth, Jupiter, or Uranus? The featured animation shows a ball dropping from one kilometer high toward the surfaces of famous solar system bodies, assuming no air resistance. The force of gravity depends on the mass of the attracting object, with higher masses pulling down with greater forces. But gravitational force also depends on distance from the center of gravity, with shorter distances causing the ball to drop faster. Combining both mass and distance, it might be surprising to see that Uranus pulls the ball down slightly slower than Earth, despite containing over 14 times more mass. This happens because Uranus has a much lower density, which puts its cloud tops further away from its center of mass. Although the falling ball always speeds up, if you were on the ball you would not feel this acceleration because you would be in free-fall. Of the three planets mentioned, the video demonstrates a ball drops even faster on Jupiter than either Earth and Uranus. via NASA https://ift.tt/2XLA42C

PDS 70: Disk, Planets, and Moons

It’s not the big disk that’s attracting the most attention. Although the big planet-forming disk around the star PDS 70 is clearly imaged and itself quite interesting. It’s also not the planet on the right, just inside the big disk, that’s being talked about the most. Although the planet PDS 70c is a newly formed and, interestingly, similar in size and mass to Jupiter. It’s the fuzzy patch around the planet PDS 70c that’s causing the commotion. That fuzzy patch is thought to be itself a dusty disk that is now forming into moons — and that has never been seen before. The featured image was taken by the Atacama Large Millimeter Array (ALMA) of 66 radio telescopes in the high Atacama Desert of northern Chile. Based on ALMA data, astronomers infer that the moon-forming exoplanetary disk has a radius similar to our Earth’s orbit, and may one day form three or so Luna-sized moons — not very different from our Jupiter’s four. via NASA https://ift.tt/3yiEY40