Alan Stern: You know for our parents’ generation of scientists, there were lots of first missions
to new places to be a part of, to be first to Mars and Venus and Jupiter and Saturn and
all that.
And by the time I got out of graduate school, Pluto was really the only one left, and even
though the missions that I’ve worked on otherwise that go back and do orbiters and
landers and so forth are great science.
It was just irresistible to get on what we used to call the first mission to the last
planet.
Loren: This is Alan Stern, the project leader of the New Horizons mission, which flew by
Pluto on July 14th, 2015.
It marked the first time a vehicle had ever visited the dwarf planet, and nearly a year
later, the mission is still giving us crazy amounts of detail about this tiny world at
the edge of the Solar System.
What had we known about Pluto before the mission even got started.
What was the extent of our knowledge?
Well we knew some really interesting things.
For example, we knew Pluto was really a binary planet with a moon half its own size and that
there’s nothing else like it we’d seen anywhere else in the solar system.
That and the system probably formed like the Earth’s Moon through a giant impact, which
again is super interesting because there’s none other analogue for the formation of the
Earth’s Moon system except way out there at Pluto.
Loren: Pluto is located in a region of the Solar System called the Kuiper Belt.
It’s a big cloud at the edge of our galactic neighborhood, filled with tiny icy bodies
ranging from the size of Manhattan to the size of whole countries.
Scientists used to think Pluto was the only tiny world orbiting beyond Neptune, when it
was first discovered in 1930 by Clyde Tombaugh.
But in the 1990s, researchers started finding more objects and even more dwarf planets in
this Kuiper Belt region.
Alan Stern: It became obvious to planetary scientists even the whole national academy
that there was this third class of planet in the solar system and that Pluto was the
harbinger of that.
Loren: Because of Pluto’s potential as a destination, a planetary survey in the early
2000s listed the dwarf planet as the number one priority for space exploration among the
scientific community.
The report helped to secure funding for the New Horizons mission, which launched in January
2006.
Alan Stern: New Horizons was launched on a very, very large expendable launch vehicle
in 2006, called an Atlas V. In fact, we bought the most souped up, tricked up version of
it you can get, with every add-on, every-rocket, lightweight nose cone, everything….
it ended up being the fastest spacecraft ever launched.
And we flew it to Jupiter first where Jupiter’s gravity gave it a slingshot to make it go
even faster so that we could cross the entire solar system in nine years.
Loren: New Horizons stayed in hibernation mode throughout most of its journey to Pluto,
with its last hibernation ending on December 6th, 2014, just one month before the spacecraft
entered its approach phase in January.
That’s when things started to get exciting — and a bit scary.
Alan Stern: We had to fly through one little window in space that’s only 60 by 100 miles
across and you could not arrive more than nine minutes early or nine minutes late after
a nine year journey.
So somebody did the math and said that that aim is equivalent to hitting a golf ball from
LA to New York and landing in a soup can in Manhattan.
So we we were taking images of Pluto on approach against the star fields and shipping them
back to Earth by radio and having teams analyze those to see how far we were off course and
to compute engine burn corrections.
Loren: As New Horizons got closer and closer to Pluto, photos taken by the spacecraft showed
the dwarf planet in clearer detail.
The images revealed the diverse shading and geography of Pluto, as well as the presence
of large heart-shaped region on its surface.
Finally after six months of approaching, and one terrifying software glitch, it was time
for New Horizons to execute its primary mission.
Alan Stern: it was really just the right words just to say it was emotional.
Um, we had put so many years and so much of our, our lives into that, and in as much as
you practice with ground simulations or with software simulations, as much as we tested
it on the ground, we knew it came down to just one day.
And at the same time, most of us were pretty exhausted.
We’d been working seven days a week, very long days, for many weeks on approach, because
in addition to taking care of the spacecraft and looking under every rock, there was also
new data landing all the time, and the press was interested in hearing about it, so we
had to quickly analyze it.
Loren: The day of the flyby consisted of two big moments.
There was the time of the actual flyby, which occurred at around 7:50AM ET that morning.
And then there was the time when the scientists got a signal back from New Horizons, confirming
that the flyby really happened.
That didn’t happen until after 9PM.
AS: There’re always unknown unknowns and the New Horizons was traveling so fast that
if we’d run into just one little rock pellet in orbit around Pluto the size of a rice grain
it would be game over and we’d never hear from it again….So in the morning we all
knew the spacecraft had gone by, but because the spacecraft was busy taking data while
it was there, it wasn’t talking to us until many hours later, and then the signal from
the spacecraft took almost five hours to get back to the Earth.
So we knew down to the minute when the moment of truth would come and we were ready for
it.
And when New Horizons checked in and all the signals were green, it was awesome.
LOREN VO: During the flyby, New Horizons took over 450 different observations of the Pluto
system.
The spacecraft has a big memory bank for storing this data, but a less powerful communications
system for sending it all back to Earth.
AS: We took a lot of data, but we’re sending it back at slow speeds, so it takes more than
a year for it all to get shipped back to Earth.
And even here as we do this interview, we’ve still got months to go.
And there are a lot of goodies up there and no one knows what discoveries are in it.
Every week, new data lands and and we open those packages and see what’s inside.
And it’s been, there’s never been a mission really like that.
LOREN VO: And the data so far has shown Pluto to be something of an anomaly.
AS: Normally smaller and smaller worlds have less and less going on.
And that’s the norm, when you look at for example the moons of Saturn and Uranus and
Neptune.
The bigger ones are a lot more interesting than the smaller ones that on bigger planets
tend to be a lot more active than the smaller ones that occur from Earth to Mercury um or
Mars to Ceres or what have you.
And then we get to Pluto and we found well there’s the exception to the rule.
It’s every bit as complicated as the Earth or Mars and on top of it the thing is active,
it should have cooled off by now.
It’s four billion years on and it’s just roaring with geologic activity and atmospheric
activity.
Given how much we’ve learned from New Horizons, Stern says we need to make even more spacecraft
just like it.
AS: It would be super if we could build a next generation set of missions like New Horizons,
three or four more and fly them to other small planets and sample the diversity of that crazy
part of the solar system.
We spent dozens of missions going to Mars and Venus and even Jupiter’s up around ten
missions now.
This is the biggest zone in the solar system, the most populous zone in the solar system,
it’s where most of the planets lie.
They’re of this really strange type that Pluto is and I think they easily deserve several
more exploration missions.