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July 14, 2020

The PI's Perspective: July 2015 - When the Solar System Saved the Best for Last

As you read this, the New Horizons spacecraft is cruising through the Kuiper Belt, completely healthy, conducting observations of the local heliospheric and Kuiper Belt dust environment.

Last month we released the first images showing nearby stars seen in different positions than we see them from Earth. (The storied Voyagers could have made similar images, but never did.) This is caused by the parallax effect, which you can see for yourself by raising a finger at arm's length and watching it shift back and forth as you switch which eye is viewing it. Parallax shifts in star positions have been measured for centuries, but they are minute — the largest are only about 1/1000th of a degree because the stars are too far away. But at well over 4 billion miles from Earth, New Horizons now sees the nearest stars shifted by much larger amounts. As a result, our NASA spacecraft sees an alien sky we cannot see from here on Earth. Is that about the coolest nerdiest thing you've heard in a while, or what?

The principle behind the New Horizons parallax project is illustrated in the image at left. The right image shows the results, as the nearest star, Proxima Centauri, jumps back and forth against more distant stars in images made from Earth and New Horizons, over 4 billion miles away. (Credit: NASA/Johns Hopkins APL/Southwest Research Institute; graphic: Pete Marenfeld, NSF's National Optical-Infrared Astronomy Research Laboratory)

While New Horizons flies onward, our team has been cranking out new results in scientific publications about our flyby targets in the Pluto system and the Kuiper Belt object (KBO) Arrokoth. Using the giant Japanese Subaru telescope atop Mauna Kea in Hawaii, the science team is also searching for new KBOs to study in the distance or even to fly by. Meanwhile, our operations team has been guiding the spacecraft through a series of maneuvers to study these KBOs and creating software enhancements that, once we transmit them to the spacecraft next year, will give New Horizons some impressive new scientific capabilities.

All is well, and very busy, for the mission team.

A Fantastic Flyby

I want to take the opportunity of mid-July 2020 to focus for a minute on mid-July in 2015, when our team and our bird made the first exploration of Pluto, the farthest planet known at the dawn of the space age. And what an absolutely amazing set of worlds Pluto and its five moons turned out to be!

As the title of this blog says, I think the solar system literally saved the best for last with Pluto. Of course, I'm a little biased -- as we all are on New Horizons -- but I can't think of a more beautiful and scientifically richer way to have completed the first era of the reconnaissance of the planets, which NASA started in 1962 with the first visit to any planet – Venus.

My strongest memories of that week are of our team's many years of hard work paying off, and of the excitement I saw in every single team member as the first detailed images of Pluto and its largest moon, Charon, came to Earth.

New Horizons team members, gathered at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, react to seeing Pluto close up for the very first time, on the morning of July 14, 2015. (Image credits: NASA/Johns Hopkins APL/Southwest Research Institute; top left: Michael Soluri)

It took 16 months to transmit all the Pluto system data back, but by late 2016, the entire haul of precious data was here on Earth. Now, after five years of work to analyze those data, our appreciation and understanding of Pluto and its moons just continues to multiply. More than 100 refereed scientific papers have been published, and a 1,000-plus-page scientific review compendium, largely by authors on the New Horizons team, summarizing basic results and interpretations of data from the Pluto flyby, is nearing publication too.

The binary planet system Pluto-Charon, first seen up close by New Horizons. (NASA/Johns Hopkins APL/Southwest Research Institute)

Pluto as seen on departure by New Horizons, backlit by the Sun. (Credit: NASA/Johns Hopkins APL/Southwest Research Institute)

And, not surprisingly, the results keep pouring in as more detailed analysis and computer modeling teach us more and more about Pluto itself, specifically its geology, chemistry, atmosphere, moons and origin.

Going back to just before the flyby, who could have predicted that not one but all of the following (and more!) would be discovered?

  • Four separate lines of evidence pointing to a liquid water ocean inside Pluto.
  • Forensic evidence in an apparently frozen lake that Pluto's atmosphere waxes and wanes, and is sometimes thicker than the atmosphere of Mars.
  • The discovery of the largest glacier in the solar system, spanning an area larger than Texas and Oklahoma combined – and that this glacier roils in thermally driven convective motion.
  • Images indicating at least two different kinds of cryovolcanism on Pluto, one or maybe both of which may have extruded organics from Pluto's subsurface water ocean.
  • Clues in Charon's dark red northern polar cap that some of Pluto's atmospheric methane escapes and becomes trapped onto the moon.
  • Areas on Pluto's surface almost as old as our 4.5 billion year old solar system, to terrains 10,000 times younger, born perhaps no more than hundreds of thousands of years ago.
  • And a sci-fi-like assortment of methane snowcapped mountains, giant canyon systems, strangely aligned, bladed mountain ranges, ground fogs, and layered atmospheric hazes in Pluto's blue sky.
And those are just the tip of the iceberg of discoveries made at Pluto! Any one of these alone would have been worth the journey. But discovering them all? No Christmas or Hanukkah could have brought better presents than this!

It's hard to believe that was five years ago; the time since has literally flown by to me. And these results have been so impactful in the field of planetary science that missions are being studied in preparation for the new Planetary Decadal Survey to go back to Pluto and the Kuiper Belt with even more powerful sensors aboard a Pluto orbiter. By the time we mark the 10th anniversary of the Pluto flyby in July 2025, such a mission could even be under construction.

Meanwhile our exploration of the Kuiper Belt and KBOs with New Horizons is far from complete. Next time, I'll give an update on the results of those telescopic searches we're making for new KBO targets for New Horizons.

With that, I'll conclude this report. In the meantime, I hope you'll keep on exploring — just as we do!

–Alan Stern

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