New Horizons flyby of Pluto [updated for Ultima Thule]

[1oldman2]

A great article by Emily, too long to post but the link is highly recommended reading.
http://www.planetary.org/blogs/emily-lakdawalla/2016/10251718-dpsepsc-new-horizons-pluto.html

Last week's Division for Planetary Sciences/European Planetary Science Congress meeting was chock-full of science from all over the solar system. A total of five sessions (one plenary, three oral, and one poster) was devoted to New Horizons at Pluto. It's been a year since the flyby, a year that early science has had a chance to mature. What's changed about our understanding of Pluto in that time?

First of all, an important reminder: New Horizons didn't return its data instantly. We were told it would take 16 months to get all the data down. It took slightly more than that, but the data transmission is now complete, as of last weekend. Hats off to the New Horizons team for not only accomplishing the flyby, but safely returning all the data!

Of course, because data transmission took so long, scientists kept needing to modify analyses to incorporate freshly returned data. It's like an image progressively coming into focus -- the early data gave the team a good sense of what they had, but later data added depth and detail.

I'll give some science summaries below, but first I want to share some news about data release, as well as a pretty picture. In his plenary talk, principal investigator Alan Stern announced that the second delivery of data to the Planetary Data System will come this month. This is going to include a lot of the nicest photos that New Horizons took through both high-resolution LORRI and lower-resolution-but-color MVIC cameras, and it was all downlinked without lossy compression, so it will be an exciting data release. There are two more releases planned for Pluto flyby data, in April and September 2017. Stern also mentioned that NASA has just announced a Data Analysis Program (DAP) for New Horizons, meaning that researchers not on the team can now propose for grant funds to work on the mission's data. Finally, Stern and many other team members shared this absolutely gorgeous color map of Pluto's surface, remarking on how you can see Pluto's color changes strongly with latitude:

 

[1oldman2]

Halfway point to the next show, New Horizons is giving us our moneys worth.

https://blogs.nasa.gov/pluto/2016/12/22/exploring-pluto-and-a-billion-miles-beyond/

As 2016 ends, I can’t help but point out an interesting symmetry in where the mission has recently been and where we are going. Exactly two years ago we had just taken New Horizons out of cruise hibernation to begin preparations for the Pluto flyby. And exactly two years from now we will be on final approach to our next flyby, which will culminate with a very close approach to a small Kuiper Belt object (KBO) called 2014 MU69 - a billion miles farther out than Pluto - on Jan. 1, 2019. Just now, as 2016 ends, we are at the halfway point between those two milestones.

http://blogs.nasa.gov/pluto/wp-content/uploads/sites/253/2016/12/KBO-Paper-from-NH.jpg

 

[1oldman2]

The "New" New Horizons News,
https://www.nasa.gov/feature/new-mysteries-surround-new-horizons-next-flyby-target
"These results are telling us something really interesting," said New Horizons Principal Investigator Alan Stern, of SwRI. "The fact that we accomplished the occultation observations from every planned observing site but didn’t detect the object itself likely means that either MU69 is highly reflective and smaller than some expected, or it may be a binary or even a swarm of smaller bodies left from the time when the planets in our solar system formed."

 

[DaveC426913]

a "small and highly reflective" object drifting in the outer solar system eh?
Hmmm...
Isn't this is the way so many sci-fi stories start?

 

[rootone]

Daleks!

 

[1oldman2]

a "small and highly reflective" object drifting in the outer solar system eh?
Hmmm...
Isn't this is the way so many sci-fi stories start?

Yup, talk about a potential story line.

 

[OmCheeto]

Daleks!

Ramans!

NASA; "Initial estimates of MU69’s diameter, ... fall in the 20-40 kilometer range ..."

A.C. Clarke; "...Rama is a perfect cylinder, 20 kilometres in diameter and 54 kilometres long, and completely featureless"

 

[1oldman2]

Ramans!

NASA; "Initial estimates of MU69’s diameter, ... fall in the 20-40 kilometer range ..."

A.C. Clarke; "...Rama is a perfect cylinder, 20 kilometres in diameter and 54 kilometres long, and completely featureless"

Good book!

 

[1oldman2]

https://www.nasa.gov/feature/nasa-s-new-horizons-team-strikes-gold-in-argentina

 

[lpetrich]

NASA’s New Horizons Team Strikes Gold in Argentina | NASA

A primitive solar system object that’s more than four billion miles (6.5 billion kilometers) away passed in front of a distant star as seen from Earth. Just before midnight Eastern Time Sunday (12:50 a.m. local time July 17), several telescopes deployed by the New Horizons team in a remote part of Argentina were in precisely the right place at the right time to catch its fleeting shadow — an event that’s known as an occultation.

That's 2014 MU69, New Horizons's next destination, in a flyby on 2019 Jan 1. So far, there are five confirmed observations of this occultation.

No report on size estimates from this occultation, though the article states for this KBO "likely 14-25 miles or 22-40 kilometers across". The occultations will also be good for getting a line of sight for this KBO, to help NH aim its cameras at it.

 

[mfb]

New Horizons' cameras could image Pluto better than Hubble something like 3 months before the fly-by, at that time it got a few pixels from a 2300 km object. As its speed will be nearly the same at MU69, we can expect to see some features just one day before the fly-by, at a distance of about 1 million km. While spectroscopy and searches for moons can be done before and afterwards as well, the whole imaging phase is just two days long. This also means New Horizons has to do most of it automatically. Light-speed delay is 6 hours per direction and the signal transmission rate is very low. By the time the scientists get the first pictures with relevant spatial resolution and can react to it, New Horizons will be very close to the object already.

 

[1oldman2]

Updates, the show ain't over yet. MU69 may not be the end of the fun.
https://spaceflightnow.com/2017/09/...lyby-plan-for-new-horizonss-next-destination/
"We expect to put a second extended mission proposal into senior review about that time," Stern said. "We are currently searching for new close flyby targets, and we have some very promising techniques and enough fuel... that we’ve got a fighting chance of having a second KBO flyby."
"Mission planners initially budgeted propellant for New Horizons to fine-tune its speed toward MU69 to better match the object’s rotation and improve visibility for the craft’s cameras. But scientists now believe the probe is approaching MU69 along its rotational axis, eliminating the need for additional rotational phasing maneuvers and saving fuel to reach another target in the 2020s."

 

[1oldman2]

Light-speed delay is 6 hours per direction and the signal transmission rate is very low.

From the same article. ( And I thought my downlink speed sucked.)
"Once the probe’s dish-shaped antenna is trained back on Earth, imagery and data will begin to trickle down soon after the flyby, making the six-hour trip at light speed at a rate of just 1 to 2 kilobits per second. At that downlink speed, it will take more than a year-and-a-half to return all the scientific goods gathered by New Horizons."

 

[Borg]

Two days to the next target for New Horizons - Ultima.

 

[mfb]

The object has a diameter of just 30 km and New Horizons is planned to pass it at 3000 km distance at a speed of about 15 km/s. Similar to Pluto: The phase of closest approach is much shorter than the light speed delay (just about 10 minutes in this case).

 

[diogenesNY]

Double potato! Oh yeah!

http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20190102

diogenesNY

 

[fizzy]

Double potato: aka contact binary.

I worked out that this was a binary and not a "bowling skittle" from the 3 pixel wide image they posted on 1s Jan. I also think it has a large dark area ( probably impact crater ) on the side shown in that image. It seems the latest image with more useful resolution , linked above, is the other side of the MU69 due to its 15h rotation.

We will see, hopefully tomorrow, a more detailed image of the same side as Jan 1st shot.

I read that one of the NH team said that there was enough gravitational attraction to hold the two lumps together, which gut feeling seemed a little surprising with a 15h rotation. What kind of force is there holding these together?

 

[alantheastronomer]

From the image, it seems that the accretion of small bodies in the early solar system was achieved through the adhering of ices on the mutual surfaces, be they water ice, carbon dioxide, methane or nitrogen...

 

[OmCheeto]

...
What kind of force is there holding these together?

Gravity.

Btw, this is an entertaining problem. It took me a couple of hours to solve.

Mostly because of the little details that I don't know how to solve off the top of my head:

barycenter
center of gravity
centrifugal force​

ps. No guarantees that this is correct.

 

[Janus]

Gravity.

Btw, this is an entertaining problem. It took me a couple of hours to solve.

View attachment 236760

Mostly because of the little details that I don't know how to solve off the top of my head:

barycenter
center of gravity
centrifugal force​

ps. No guarantees that this is correct.

Assuming your numbers are at least reasonably correct and using a rotation period of 15h, I get a centripetal acceleration of 0.00016 m/s² to hold Thule to Ultima against the spin (as measured at its center). the centripetal acceleration of Thule due to the gravitational pull of Ultima (center to center) is 0.0009 m/s² or ~5.7 times larger. At the far end of Thule, the required centripetal force increases to 0.00025 m/s² and gravity decreases to 0.0007m/s²; But it is still enough to hold on to something against the spin.

 

[fizzy]

thanks for the replies. In the context of its paragraph talking about gravitational attraction my qu. "what sort of force" meant what sort of magnitude is the force, not where does it come from.

When two bodies are touching using two point masses is obviously not right but does at least give a first order approximation. Thanks for the numbers.

I downloaded a presentation from NH and they seem to use the density of water. Presumably they are assuming this is mainly water ice plus some rocky dust.

Hopefully later today we will get a new image with the other side and we will see whether I was correct about there being a large dark feature, or whether that was just an image processing artefact.

 

[fizzy]

hmm, now into 5th Jan in Europe and still nothing newer than the 1st Jan "snowman" image. I thought they were supposed to be publishing one a day.

http://pluto.jhuapl.edu/soc/UltimaThule-Encounter/

"In the images posted on Jan. 1, Ultima is expected to be approximately 3 pixels across, but it will grow to approximately 100 pixels across for the images posted on Jan. 2, and approximately 200 pixels across for the images posted on Jan. 3."

 

[fizzy]

Very odd. Closest approach was on Wed 3rd Jan but their NH twitter feed is still pumping out the boring "snowman" image from 1st Jan.

What is going on here? Has the data link gone down or are NASA playing hide-and-seek with the publicly owned images again?

 

[mfb]

Data transmission takes time, high resolution images need longer than low resolution images, and there is much more to transmit than just pictures. In addition NASA has no obligation to release pictures as soon as they arrive here just because you want to see a new picture every day.

 

[OmCheeto]

There are also the limitations of the Deep Space Network.
All 11 antennas are currently assigned to other craft.

 

[Klystron]

Consider also the missing paychecks of many Federal employees and contractors coupled with holidays.
https://www.nytimes.com/2019/01/05/us/government-shutdown-science.html

 

[glappkaeft]

Very odd. Closest approach was on Wed 3rd Jan but their NH twitter feed is still pumping out the boring "snowman" image from 1st Jan.

What is going on here? Has the data link gone down or are NASA playing hide-and-seek with the publicly owned images again?

From: http://www.planetary.org/blogs/emily-lakdawalla/2019/mu69-baby-comet-contact-binary.html

No further images will come to Earth from New Horizons until January 10 because the spacecraft is behind the Sun, making radio communication error-prone.

 

[fizzy]

Ah thanks. Since we are at perihelion now that means this MU69 object is almost exactly along the Earth's line of apsides. Coincidence, or did they chose that path out of the inner SS for a specific reason? It will be interesting to see more detail over the next few weeks.

At least I can stop going back every day hoping there an update. Shame they did not explain this on the NH page where they post the new images.

It's also a shame they only give up crappy jpegs instead of the option of a non lossy format which would be more use for playing around with image processing.

Thanks for the info.

 

[OmCheeto]

Well, I found a gravity bug in my method, yielding somewhat different numbers.

At the far end of Thule, the required centripetal force increases to 0.00025 m/s2 and gravity decreases to 0.0007m/s2

My gravity number is 4 times larger than yours at the Thule end.
Even discounting the gravity from Ultima, my value is still 3 times higher than yours.
g = 1.5e15 kg * 6.674e-11 / (7000 m)^2 = 0.002043 m/s^2

0.002043 / 0.0007 = 2.9

What am I doing wrong?

 

[mfb]

Ah thanks. Since we are at perihelion now that means this MU69 object is almost exactly along the Earth's line of apsides. Coincidence, or did they chose that path out of the inner SS for a specific reason? It will be interesting to see more detail over the next few weeks.

Coincidence. The main trajectory was based on the Pluto approach, afterwards they searched for something that can be reached with minimal fuel consumption.

The trajectory at Pluto was chosen to get a gravity assist at Jupiter, to get a good view of the day side with a close fly-by, a good view of Charon, a pass through Pluto's shadow (to measure the atmosphere), to have Pluto between probe and Earth (for radio measurements) and to have Charon behind Pluto to have some light on its night side. That a trajectory exists with all these features is amazing already.

 

[fizzy]

Well, I found a gravity bug in my method, yielding somewhat different numbers.

My gravity number is 4 times larger than yours at the Thule end.
Even discounting the gravity from Ultima, my value is still 3 times higher than yours.
g = 1.5e15 kg * 6.674e-11 / (7000 m)^2 = 0.002043 m/s^2

0.002043 / 0.0007 = 2.9

What am I doing wrong?

You are using billiard ball physics but your "centre" of mass seems to be at the point they touch.

If you want to simply to two point masses they are separated by 7+9.5km
If you want the effect of one mass at the outside to the other it's its radius plus the diam of the other.

BTW inverse square law can only be applied "far field" , ie. where the diameters are much smaller than the separation between them.

 

[mfb]

Inverse square law is exact everywhere outside of spherically symmetric objects (within Newtonian mechanics). Didn’t pay much attention to that discussion part so far but if there is still something unclear I can have a look.

 

[fizzy]

"Inverse square law is exact everywhere outside of spherically symmetric objects"
It is good enough for a first approximation but it is certainly not exact.

Consider a test mass one radius from a spherical body. Work out the contributions form two points diametrically opposed on the surface, once is distant by r , the other by 3r. Compare that to the same masses placed a the centre of mass.

1/r^2+1/(3r)^2 = 2/(2r)^2 ??

A similar inequality and of the same sign will apply for all pairs of points symmetrically placed either side of the plane through the c.o.m. and perpendicular to the line joining the test mass and the centre. Summing all such pairs to represent the whole shows the inequality holds for the whole body.

The inaccuracy reduces as the separation becomes much larger than the diameter of the sphere.

 

[mfb]

It is exact. You can't limit the calculation to two points, you have to integrate over the whole shell. Do it and see what you get.
Alternatively: It is a direct consequence of Gauss' law.

This is a well-known result from classical mechanics and not the topic of this thread. If you have more questions about it please start a separate thread.

 

[fizzy]

fair point:
https://www.physicsforums.com/threads/is-inv-sqr-law-exact-near-to-a-spherical-body.963631/

 

[OmCheeto]

I also started another thread on the math problem: https://www.physicsforums.com/threads/net-forces-on-ultima-thule.963691/

 

[OmCheeto]

And, we're back in business.

Not sure how long it will take to download the next image. I guess it depends on how big the file is.

 

[Borg]

Could you post the link to that page, Om?

 

[OmCheeto]

Could you post the link to that page, Om?

https://eyes.nasa.gov/dsn/dsn.html

Btw, it's possible they were just checking for a signal when I checked, and got nothing but noise.
Currently, only 3 of the 12 dishes are in use, and New Horizons is not one of them.

 

[mfb]

Canberra (43) is receiving data from New Horizons right now. 2 kb/s downlink at 8.44 GHz, 500 b/s uplink at 7.18 GHz.

Edit: Canberra tweeted it, too

 

[glappkaeft]

New images released: http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20190115

Better images will be availible in late Februari: https://twitter.com/AlanStern/status/1085236157565276162

 

[mfb]

We got a new picture now already.

Article

Full resolution

 

[DrClaude]

Pancakes!

https://apod.nasa.gov/apod/ap190211.html
http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20190208