Published: 2015-07-14 06:03:00
Updated: 2015-07-14 07:29:47
Posted July 14, 2015
By Tony Rice
Even before New Horizons makes its closest approach to Pluto on July 14 at 11:49:57 UTC (7:49:57 a.m. EDT), the mission has already rewritten textbooks on the once planet and the third zone of the solar system where it lives, the Kuiper belt.
Recent images showed the true diameter of Pluto to be 2,370 km (1,473 miles) in diameter +/- about 20 km. Previous measurements attempts have been hampered by mirages created by Pluto’s thin atmosphere, making the true edge of the planet difficult to see.
Planetary mass is much easier to determine (based on orbital behavior of neighboring objects), and Eris has Pluto beat there. This means that there is more ice is layered in Pluto’s crust than previously expected. The presence of that ice likely means that Pluto’s troposphere, the lowest later of its atmosphere, is likely closer to the surface that previous models suggested.
Mike Brown, who led a team of CalTech astronomers in discovering Eris along with 15 other trans-Neptunian objects, tweeted about the finding this week from his @plutokiller account: “Odd that Eris is a tiny bit smaller than Pluto but so much more massive. They are quite different bodies in many ways. Maybe we should go.”
Pluto's upgrade to largest Kuiper Belt object has left some wondering if it might pave the way for a promotion back into the planetary big leagues. Unfortunately that isn’t enough. Pluto is still Pluto regardless of it’s label. It fails to meet the definition of a planet established at the International Astronomical Union (IAU) meeting in 2006. But all that has and will continue to be discovered by this mission will keep discussion of Pluto's label alive.
Once New Horizons passes Pluto, its job is far from done. By mid-afternoon Tuesday here on Earth, the spacecraft will take advantage of four occultations to study the atmospheres of Pluto and its largest moon, Charon. Occultations occur when a planet passes in front of another body, usually a star. Astronomers use events like this to observe light as a planet or moon passes in front of a star, studying how light changes changes.
New Horizons will pass through the shadow cast by Pluto shortly before 9 a.m. EDT and Charon around 10:20 a.m. EDT. Pluto and Charon will also cast a radio shadow around the same times as Pluto passes between the spacecraft and Earth, enabling study of signals sent by NASA’s giant 70-meter Deep Space Network dish in Goldstone, Calif. Occultation observations are expected to reveal details about the composition of Pluto’s thin atmosphere and reveal whether Charon has one at all.
While the mission will make its final observations of the Pluto system early next week, the spacecraft works on. The next 19 months will be spent slowly transmitting findings back to Earth. This is a slow process, with only about 1 kilobit per second possible due to the weak signal arriving from 3 billion miles away. For instance: a single 1024x1024 pixel black and white image from the LORRI camera onboard takes about 43 minutes to transmit. New Horizons has more than 2,000 observations just from this week to return.
Once that data transmission is complete, the team will move on to ask NASA to extend New Horizons on to another campaign, visiting other objects deeper in the Kuiper Belt.
You can join in free “PlutoPalooza” events in the triangle during the period of closest fly-by this week:
Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.