Mission Elapsed Time:
(Beginning 1/19/06 19:00:00 UTC)
2667 Days (7.31 yrs.) 06 Hours 14 Minutes
Pluto Closest Encounter Operations Begin:
(4/12/15 00:00:00 UTC)
701 Days (1.92 yrs.) 22 Hours 45 Minutes
Pluto Closest Approach:
(7/14/15 11:49:59 UTC)
795 Days (2.18 yrs.) 10 Hours 34 Minutes
New Horizons Current Position and Course in Three Dimensions:
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A new companion for Neptune:
Alex Parker and associates describes a serendipitous discovery that his collaborators and he made while searching for a distant Kuiper Belt Object for the New Horizons spacecraft to visit after its 2015 Pluto flyby.
So, what kind of serendipitous discovery did they make? They found a Neptune Trojan, now called 2011 HM102. It is not just any Neptune Trojan: It's the largest trailing Trojan known in the entire Solar System, it's the most inclined Neptune Trojan known, and (as of right now) it is the closest known object of any kind to the New Horizons spacecraft
Trojans in the Solar System:
Trojan asteroids are objects in 1:1 mean-motion resonance with a planet, meaning that they orbit with (nearly) exactly the same period as the planet. There are different semi-stable orbital configurations for objects in 1:1 mean-motion resonance, and Trojans are objects which fall into two of these configurations - namely, they lead or trail the planet in its orbit by (on average) about 60 degrees. Objects leading the planet oscillate around the planet-Sun are called the L4 Lagrange point, while objects trailing the planet oscillate around the planet-Sun are called the L5 Lagrange point. This kind of orbital oscillation is called "liberation."
The distant ice-giant Neptune has nine known stable Trojans. While at first glance it might seem that since we know of more than 5000 Trojan companions for Jupiter and only nine for Neptune, we can give Jupiter the award for having the most Trojans today. Neptune is much farther away from us than Jupiter, and it is much harder to detect small objects (like Trojans) at Neptune's distance than it is at Jupiter's. Early estimates correcting for this effect indicate that Neptune's Trojan swarms may have upwards of 10 times as many objects in them as Jupiter's swarms, or equivalently 10 times as many objects as reside in the Main Asteroid Belt. The trick is finding these distant, slow-moving, and exceedingly faint objects. Which brings us to why were they at the telescope when they found 2011 HM102? Well, we have a spacecraft called New Horizons and it is planned that after its successful run at Pluto it will take a look at some KBOs already picked out ahead of time. New Horizons is currently flying out to meet Pluto at a breakneck speed of over 13 kilometers per second. In July of 2015, it will fly through the Pluto system, collecting as much data as it can with its onboard instruments, and then beam all that information back to Earth. However, there's no stopping New Horizons at Pluto. The spacecraft will continue outward into the Kuiper Belt at that incredible speed, with enough fuel left onboard for a small course change. The goal is to find a small Kuiper Belt Object (KBO) for New Horizons to study once it has completed its primary mission to Pluto. Because of its limited remaining fuel supply, it can only make a small course change, meaning that it can only reach a very small slice of the outer Solar System. However, the outer Solar System is filled with billions of small, icy objects, and a few of these may be the perfect candidates they are looking for.
Astronomers conducting surveys for KBOs usually pick fields far away from the Galactic plane to avoid dealing with images filled to the brim with boring old stars. So, unfortunately, that means they have to do a special survey, and they got to deal with the nightmare that is dredging through these star fields for moving objects. Starting in 2011, they have been turning these telescopes and their giant imaging arrays toward the patch of sky where they expect to find the Kuiper Belt objects that New Horizons can reach.
Once these images have been collected the images are scrutinized for targets. Special techniques are applied that remove stationary objects (like stars) and reveal moving objects (like Kuiper Belt objects).
Discovery of 2011 HM102:
Their survey beam punched right through Neptune's trailing Trojan cloud. The survey was not designed specifically to find Neptune Trojans – though they were aware that they could find them During the normal search process, they spotted 2011 HM102 as fast-moving and very bright - it's the brightest object discovered to date by a wide margin.
Using the updated orbit, a large number of simulations were run to determine how stable 2011 HM102 was, and found that for at least a billion years, 2011 HM102 happily continues to remain in its resonant configuration with Neptune. Because 2011 HM102 is quite bright (compared to the other objects they had been finding), they could also measure it's color. This is done by collecting images of the object through various color filters, and comparing how bright it appears in one color filter versus another. This was the first measurement of the color of a trailing Neptune Trojan, and it was demonstrated that it has a very similar color to the leading Neptune Trojans.
They recognized one other interesting aspect about 2011 HM102: it comes fairly close to New Horizons position as it heads for Pluto. As of right now, it is the closest known object of any kind to New Horizons - about 2.5 AU away. In the later parts of 2013, it will pass within 1.2 AU of New Horizons, where it will be bright enough to be just detectable from New Horizons.
