Transit Of Venus

The Van Allen Belt & the 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.

The near-Earth 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

Largest Batch of Earth-size, Habitable Zone Planets

Our Spitzer Space Telescope has revealed the first known system of seven Earth-size planets around a single star. Three of these planets are firmly located in an area called the habitable zone, where liquid water is most likely to exist on a rocky planet.

This exoplanet system is called TRAPPIST-1, named for The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile. In May 2016, researchers using TRAPPIST announced they had discovered three planets in the system.

Assisted by several ground-based telescopes, Spitzer confirmed the existence of two of these planets and discovered five additional ones, increasing the number of known planets in the system to seven.

This is the FIRST time three terrestrial planets have been found in the habitable zone of a star, and this is the FIRST time we have been able to measure both the masses and the radius for habitable zone Earth-sized planets.

All of these seven planets could have liquid water, key to life as we know it, under the right atmospheric conditions, but the chances are highest with the three in the habitable zone.

At about 40 light-years (235 trillion miles) from Earth, the system of planets is relatively close to us, in the constellation Aquarius. Because they are located outside of our solar system, these planets are scientifically known as exoplanets. To clarify, exoplanets are planets outside our solar system that orbit a sun-like star.

In this animation, you can see the planets orbiting the star, with the green area representing the famous habitable zone, defined as the range of distance to the star for which an Earth-like planet is the most likely to harbor abundant liquid water on its surface. Planets e, f and g fall in the habitable zone of the star.

Using Spitzer data, the team precisely measured the sizes of the seven planets and developed first estimates of the masses of six of them. The mass of the seventh and farthest exoplanet has not yet been estimated.

For comparison…if our sun was the size of a basketball, the TRAPPIST-1 star would be the size of a golf ball.

Based on their densities, all of the TRAPPIST-1 planets are likely to be rocky. Further observations will not only help determine whether they are rich in water, but also possibly reveal whether any could have liquid water on their surfaces.

The sun at the center of this system is classified as an ultra-cool dwarf and is so cool that liquid water could survive on planets orbiting very close to it, closer than is possible on planets in our solar system. All seven of the TRAPPIST-1 planetary orbits are closer to their host star than Mercury is to our sun.

 The planets also are very close to each other. How close? Well, if a person was standing on one of the planet’s surface, they could gaze up and potentially see geological features or clouds of neighboring worlds, which would sometimes appear larger than the moon in Earth’s sky.

The planets may also be tidally-locked to their star, which means the same side of the planet is always facing the star, therefore each side is either perpetual day or night. This could mean they have weather patterns totally unlike those on Earth, such as strong wind blowing from the day side to the night side, and extreme temperature changes.

Because most TRAPPIST-1 planets are likely to be rocky, and they are very close to one another, scientists view the Galilean moons of Jupiter – lo, Europa, Callisto, Ganymede – as good comparisons in our solar system. All of these moons are also tidally locked to Jupiter. The TRAPPIST-1 star is only slightly wider than Jupiter, yet much warmer. 

How Did the Spitzer Space Telescope Detect this System?

Spitzer, an infrared telescope that trails Earth as it orbits the sun, was well-suited for studying TRAPPIST-1 because the star glows brightest in infrared light, whose wavelengths are longer than the eye can see. Spitzer is uniquely positioned in its orbit to observe enough crossing (aka transits) of the planets in front of the host star to reveal the complex architecture of the system. 

Every time a planet passes by, or transits, a star, it blocks out some light. Spitzer measured the dips in light and based on how big the dip, you can determine the size of the planet. The timing of the transits tells you how long it takes for the planet to orbit the star.

The TRAPPIST-1 system provides one of the best opportunities in the next decade to study the atmospheres around Earth-size planets. Spitzer, Hubble and Kepler will help astronomers plan for follow-up studies using our upcoming James Webb Space Telescope, launching in 2018. With much greater sensitivity, Webb will be able to detect the chemical fingerprints of water, methane, oxygen, ozone and other components of a planet’s atmosphere.

At 40 light-years away, humans won’t be visiting this system in person anytime soon…that said…this poster can help us imagine what it would be like: 

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Radar Observations of Asteroid 2014 HQ124

Radar data of asteroid 2014 HQ124 taken over for hours on June 8, 2014, when the asteroid was between 864.000 miles (1.39 million kilometers) and 902.00 miles (1,45 million kilometers) from Earth. The data reveals asteroid 2014 HQ124 to be an elongated, irregular object that is at least 1200 feet (370 meters) wide on it long axis. The radar was obtained using NASA’s 70 meters Goldstone antenna, the same antenna used for communicating with spacecraft in deep space. The Goldstone radar team paired with the Arecibo Observatory (Goldstone sending radar, Arecibo receiving) for the first five frames of this movie in order to collect higher quality data resulting in shaper images. The other frames were made by both sending and receiving with antennas at the Goldstone complex.

Credit: NASA/JPL

Have Astronomers Found Alien Megastructures After All? (No, Probably Not)

“We’ve often found that — when it comes to unexpected astronomical signals — our imaginations run away with us, leading us to immediately jump to conclusions about our greatest hopes and/or fears, like the existence of sentient aliens accessible to us. But the real Universe, every time thus far, has shown itself to be more diverse, complex, and rich in phenomena than we had previously realized, including the existence of quasars, pulsars, exoplanets and more. We haven’t yet ruled out the possibility of alien megastructures, but what we’re most likely seeing is a new type of natural phenomena whose origin is yet unknown. Follow-up observations, particularly those scheduled for 2017, when another major “transit” event is scheduled to occur, should teach us a whole lot more.”

Last year, Penn State astronomer Jason Wright made headlines by claiming that one of the stars being observed by NASA’s Kepler mission might contain alien megastructures around it. The large dips in its light curve didn’t make sense in the context of planets, and the star KIC 8462852 became the target of a great many follow-ups. A binary companion was found, along with no signs of excess infrared emission or artificial radio signatures. However, archival data recently found that the star dimmed by about 20% over the past century. While the alien megastructures possibility cannot be ruled out, a great many other astrophysical possibilities still survive.

Comments of the Week #92: from the Universe’s birth to ten decades of science

“[I]f there were antimatter galaxies out there, then there should be some interface between the matter and antimatter ones. Either there would be a discontinuity (like a domain wall) separating the two regions, there would be an interface where gamma rays of a specific frequency originated, or there would be a great 2D void where it’s all already annihilated away.

And our Universe contains none of these things. The absence of them in all directions and in all locations tells us that if there are antimatter galaxies out there, they’re far beyond the observable part of our Universe. Instead, every interacting pair we see shows evidence that they’re all made of matter. Beautiful, beautiful matter.”

There’s no better way to start 2016 than… with a bang! Come check out our first comments of the week of the new year.

W. M. Keck Observatory telescopes logo. December 2, 2014

Image above: A dusty planetary system (left) is compared to another system with little dust in this artist’s conception. Image Credit: NASA/JPL-Caltech. Planet hunters received some good news recently. A...

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