Pluto explorer passes milestone distance

After more than 15 years and more than 4.6 billion miles, the New Horizon mission joins small club of spacecraft that have passed a point 50 times farther from the Sun than Earth.

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New Horizons joins 4 other spacecraft in passing 50 AU
Tony Rice
, NASA Ambassador

Saturday evening at 8:42 p.m. EDT, New Horizons passed 50 astronomical units (AU) from the Sun, or about 4.6 billion miles.  Just the fifth spacecraft to reach this great distance, it joins Voyagers 1 and 2 and with Pioneers 10 and 11 in the "50 AU club".

Launched in 2006, the baby grand piano sized spacecraft spent the next 9.5 years traveling through the solar system for a flyby of Pluto which produced spectacular images of the frozen planet.

New Horizons took on a secondary mission on New Years Day January 2019 flying past 486958 Arrokoth, a 22-mile long snowman shaped Kuiper belt object.

Wrapping your head around nearly 5 billion miles.

“One thing that makes this distance tangible is how long it takes for us on Earth to confirm that the spacecraft received our instructions. This went from almost instantaneous to now being on the order of 14 hours. It makes the extreme distance real.” said Alice Bowman, the New Horizons mission operations manager at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.

Think of the solar system like a really long neighborhood street. The Sun is the house next door, Mars is 2 houses down the street, and Pluto is 34 houses away.  New Horizons is 50 houses down the street.

Voyager 1 is in the next neighborhood, 152 houses away.

Hello, Voyager! From the distant Kuiper Belt at the solar system’s frontier, on Christmas Day, Dec. 25, 2020, NASA’s New Horizons spacecraft pointed its Long Range Reconnaissance Imager in the direction of the Voyager 1 spacecraft, whose location is marked with the yellow circle. Voyager 1, the farthest human-made object and first spacecraft to actually leave the solar system, is more than 152 astronomical units (AU) from the Sun—about 14.1 billion miles or 22.9 billion kilometers—and was 11.2 billion miles (18 billion kilometers) from New Horizons when this image was taken. Voyager 1 itself is about 1 trillion times too faint to be visible in this image. Most of the objects in the image are stars, but several of them, with a fuzzy appearance, are distant galaxies. New Horizons reaches the 50 AU mark on April 18, 2021, and will join Voyagers 1 and 2 in interstellar space in the 2040s. Image: NASA/Johns Hopkins APL/Southwest Research Institute

Still in the solar system

4.6 billion miles is a long way away, but New Horizons still well within the solar system.

Even at its current speed of over 31,000 mph, New Horizons won't reach the heliopause, or the region of space where the solar winds from other stars are stronger than the solar winds from our star, for another 25 years.

Launched in the late 1970s, both Voyager 1 and 2 remain active with about half their instruments still functional. Those instruments confirmed the missions reached interstellar space in 2012 and 2018 respectively.

When Pioneer 10 and 11, launched in the early 1970s, are probably next to reach that interstellar milestone, but exactly when is up for debate.  Scientists haven't heard from either spacecraft since 2003 so direct measurements aren't possible. 

Some research points to a long comet-like tail dominating the shape of the Sun’s bubble of influence, while an updated model suggests more of deflated croissant shape. Images: NASA’s Scientific Visualization Studio/Conceptual Imaging Lab, Merav Opher, et al

NASA's Interstellar Boundary Explorer (IBEX) mission is working out not just how far out the Sun's influence extends but the resulting shape of the solar system.  Its not a perfect circle as the heliosphere name might suggest.

While scientists have traditionally thought of the heliosphere as a comet shape, with a rounded leading edge, and a long tail trailing behind, new research suggests another explanation.

In a study published last year in the journal Nature Astronomy, study of space weather points to something shaped more like a popcorn kernel, or as lead author Marav Opher describes it a "deflated croissant".


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