Pluto is in the sights of NASA’s New Horizons spacecraft, which started collecting around-the-clock science data Thursday as it speeds toward the first close encounter with the distant world in July.

The mission’s encounter phase formally started Thursday with the activation of the probe’s dust and plasma instruments to collect information on the environment at the outer frontier of the solar system.

Photos will come later, with the first imaging campaign of the Pluto encounter set to begin Jan. 25. The imagery will not be as sharp as photos from the Hubble Space Telescope until May, when New Horizons will start taking pictures showing Pluto in unprecedented detail through the mission’s July 14 flyby.

Thursday’s milestone came the same week as the ninth anniversary of the mission’s launch from Earth on Jan. 19, 2006. New Horizons is now about 134 million miles from Pluto, a fraction of the distance separating it from Earth.

“Our knowledge of Pluto is quite meager,” said Alan Stern, the mission’s principal investigator from the Southwest Research Institute in Boulder, Colorado, during a press briefing in November. “Despite the march of technology on the ground that has given us big telescopes, very powerful spectrometers, and even the Hubble Space Telescope in Earth orbit, we know very little about this world. In a real sense, it’s very much like our knowledge of Mars before our first mission to Mars 50 years ago.”

When New Horizons zooms past Pluto on July 14 — passing 6,200 miles above its icy crust — the spacecraft’s camera will be able to see surface features as small as 70 meters (230 feet) across.

If the probe was flying over New York, Stern said images from the New Horizons camera could allow scientists to count the lakes in Central Park and wharfs along the Hudson River.

That is a big improvement over photos of Pluto obtained by Hubble, which show the faraway dwarf planet just a few pixels across.

“You can’t see very much,” Stern said. “That’s the exciting part. From my standpoint, this is a Christmas present sitting under the tree that’s been waiting while we sped across the solar system to unwrap it. We are so looking forward to turning this very fuzzy little picture of this very distant and small planet into something real, and to do it by taking the world along.”

Images taken by the craft’s LORRI telescopic camera beginning Jan. 25 will help ground controllers guide New Horizons toward Pluto, which will still appear as a dot.

The best frame-filling images of Pluto will not come until July.

“This is much more than a single day,” said Hal Weaver, the mission’s project scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “Of course, July 14, 2015, that’s the day that we reach the closest approach point to Pluto, and most of our best results will come from a few days around that time period.

“But I really want to emphasize that we’ll have lots of juicy science — historic science — accumulated well before the day of the closest approach,” Weaver said.

The milestone achieved Thursday — the start of Approach Phase 1 — is focused on taking pictures to home in on Pluto, allowing New Horizons to hit a narrow aim point designed to get the best observations of Pluto’s surface topography, composition and atmosphere.

Mission planners have allotted several opportunities for New Horizons to adjust its path toward Pluto, with the next chance for a course correction maneuver in mid-March, Stern said in an email to Spaceflight Now.

Weaver said New Horizons will also take background measurements of the particle and dust environment during Approach Phase 1, which runs through mid-April, to compare with data it collects at Pluto.

“As we move from later in April and into mid-June, that’s the time period where we start to get better than Hubble,” Weaver said. “We’ll also be doing deep searches for satellites (moons) and rings better than can be done with Hubble or any other observatory on the Earth, and then it just gets better and better and better as we’re closer and closer to Pluto.

“During the time of closest approach, it’s going to be astounding,” Weaver said. “It really will be. We’re going to be transforming Pluto from this pixelated image … into a completely new world, with complexity (and) diversity that we can’t even imagine.”

After it swoops past Pluto, New Horizons will continue taking data through the end of 2015 before taking aim on a new target in the Kuiper belt, a zone of little-studied worlds beyond the orbit of Neptune.

Then comes the data playback. It will take 16 months for all the spacecraft’s data on Pluto to stream down to the ground — a function of the volume of information scientists intend to collect and the probe’s distance from Earth.

“This is really quite an epic journey,” Stern said. “Three billion miles across the entirety of our planetary system, from the inner planets, to the middle solar system, to the third zone — the Kuiper belt — and for the first time. No voyage like this has been conducted since the epic days of Voyager, and nothing like it is planned again.”

 Wyzilla wrote:
Y'know, it's hard to get psyched for photos of Pluto. It's Pluto, a tiny planetoid orbiting the sun on the edge of our Solar System. Planets like Mars or Venus are far more interesting, and moons like Titan or Europa are breathtaking.

 AduroT wrote:
Didn't they make Pluto a planet again or I am mistaken?

 Smacks wrote:

 AduroT wrote:
Didn't they make Pluto a planet again or I am mistaken?

So far as I know the IAU still considers it to be a "dwarf planet". The decision is often criticized though. Personally I think Pluto should be classed the same as other TNOs, since they all appear very similar in constitution. Having one less planet is probably easier than having a hundred tiny new ones. Though rather than admitting that, the IAU made up an very arbitrary new definition of "planet" which might need to be revisited at some point.

(1) A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies"

 sarpedons-right-hand wrote:
This is very good news. I hope it finds something of worth though, I feel sorry for Pluto...

 ScootyPuffJunior wrote:
I don't think that the IAU's definition of a planet is arbitrary at all. It's pretty clear what being a "planet" entails.

 Wyzilla wrote:
Y'know, it's hard to get psyched for photos of Pluto. It's Pluto, a tiny planetoid orbiting the sun on the edge of our Solar System. Planets like Mars or Venus are far more interesting, and moons like Titan or Europa are breathtaking.

Although hopefully the probe discovers a black monolith on the surface of Pluto.

 Smacks wrote:

 ScootyPuffJunior wrote:
I don't think that the IAU's definition of a planet is arbitrary at all. It's pretty clear what being a "planet" entails.

The problem is 1c "has cleared the neighbourhood around its orbit". Since Pluto intersects the orbit of Neptune it could also be argued that Neptune also isn't a planet, and it is not really clear if a small planet like Mercury has really cleared its orbit, or if it just happens to be in a spot that was cleared by The Sun. Mercury and also Earth share their orbits with other objects in what is called a horseshoe pattern.

The criteria has been liken to saying what type of car you have by what the traffic around you is doing. I think as we discover more objects this definition will become problematic. A size or distance threshold might be more appropriate.

 ScootyPuffJunior wrote:
No, that's a weak argument.

Neptune has locked Pluto into a 3:2 resonance, making it gravitationally dominant. That same can be said about Jupiter's Trojans; they are only there because of Jupiter's gravitational influence.

 Darkjim wrote:
Indeed, I find any information atall about our Solar System completely fascinating. It is our tiny, tiny, tiny, tiny, tiny corner of our utterly average galaxy in a pretty damn big universe, but still so vast that Voyager has taken nearly half a century just to get to the edge. Every morsel of information is a step forward in understanding our home.

 Smacks wrote:
Well if you are forced to conflate "cleared" with "gravitationally dominate" then maybe it is the IAU definition that is weak. More distant TNOs such as Makemake are not thought to have any gravitational resonance with Neptune. Makemake was classed as a dwarf planet based on magnitude. There are also some issues with hydrostatic equilibrium, since that varies depending on composition. For example: Proteus is larger and more massive than Mimas, yet Proteus has not achieved hydrostatic equilibrium while Mimas has. If the two objects were in free orbit around The Sun (instead of being moons) then Mimas would be classed as a dwarf planet, while Proteus which is bigger would be relegated to asteroid.

I don't disagree with end result, of 8 classical planets and Pluto becoming a "dwarf planet", but I think there were problems with how the IAU arrived at that decision. There was controversy regarding the number of members that got to vote, and how things were defined. Even though they came up with this definition they haven't actually been applying it. Eris was granted dwarf planet status based on its size, Haumea was granted it based on magnitude. There are also dozens of other candidates which have not been officially recognized, and there is some controversy regarding the official recognition of any dwarf planets in the first place.

As I said before, this definition might need to be revisited later as we discover more objects and learn more about planets in other systems (exoplanets) which might contain objects that are clearly giant Planets, yet fall outside these parameters.

 ScootyPuffJunior wrote:
It's a good enough system for now, no need to change it.