Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Dawn moving to low Ceres orbit, mission extended until hydrazine runs out

  1. Dec 30, 2015 #801

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    This confirms what Om saw earlier via Twitter:
    ==quote Rayman update==
    December 29, 2015 -Flight Team Preparing Small Adjustment to Orbit

    Dawn remains in good health as it continues to take pictures and make other measurements of Ceres. As at Vesta, occasional small adjustments to its orbital motion will be required at this low altitude to keep it synchronized with the observing plan. The flight team is working on the detailed flight plan for the first of these "orbit maintenance maneuvers," scheduled for Dec. 31.
    ==endquote==
     
  2. Dec 30, 2015 #802

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    I hope they release better images of the bright spots soon, but I can imagine that they want to analyze them first.
     
  3. Dec 30, 2015 #803

    OmCheeto

    User Avatar
    Gold Member

    From some back of the napkin calculations, it looks as though it now takes about 15 days to photograph everything near the equator.
    So, I'm guessing, that if we're lucky, we will see images within a week.
    If we are not so lucky, it may be a few months.

    ps.
    Interesting article about "methane" was pointed to by the Dawn team on Facebook about an hour ago:
     
  4. Dec 30, 2015 #804

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    There are also hot rocks. Temperature is not the only reason hydrothermal vents are interesting.
     
  5. Dec 31, 2015 #805

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    http://dawnblog.jpl.nasa.gov/2015/12/31/dawn-journal-december-31/

    DECEMBER DAWN JOURNAL IS OUT!

    This journal entry is unusually visually rich with many stunning and fascinating images of Ceres' surface. Do check it out!
    But it also has this about the GRaND data being taken:
    ==quote Rayman==
    ...
    With the spacecraft this close to the ground, it can measure two kinds of nuclear radiation that come from as much as a yard (meter) deep. The radiation carries the signatures of the atoms there, allowing scientists to inventory some of the key chemical elements of geological interest. One component of this radiation is gamma ray photons, a high energy form of electromagnetic radiation with a frequency beyond visible light, beyond ultraviolet, even beyond X-rays. Neutrons in the radiation are entirely different from gamma rays. They are particles usually found in the nuclei of atoms (for those of you who happen to look there). Indeed, outweighing protons, and outnumbering them in most kinds of atoms, they constitute most of the mass of atoms other than hydrogen in Ceres (and everywhere else in the universe, including in your correspondent).

    To tell us what members of the periodic table of the elements are present, Dawn’s gamma ray and neutron detector (GRaND) does more than detect those two kinds of radiation. Despite its name, GRaND is not at all pretentious, but its capabilities are quite impressive. Consisting of 21 sensors, the device measures the energy of each gamma ray photon and of each neutron. (That doesn’t lend itself to as engaging an acronym.) It is these gamma ray spectra and neutron spectra that reveal the identities of the atomic species in the ground.

    Some of the gamma rays are produced by radioactive elements, but most of them and the neutrons are generated as byproducts of cosmic rays impinging on Ceres. Space is pervaded by cosmic radiation, composed of a variety of subatomic particles that originate outside our solar system. Earth’s atmosphere and magnetic field protect the surface (and those who dwell there) from cosmic rays, but Ceres lacks such defenses. The cosmic rays interact with nuclei of atoms, and some of the gamma rays and neutrons that are released escape back into space where they are intercepted by GRaND on the orbiting Dawn.
    ==endquote==

    It also has the latest word on the BRIGHT SPOTS on some of the crater floors. They are not pure white, many have a slight blueish tinge. The best known, the Occator crater spots, have a faint reddish tinge. It might take an instrument more sensitive than the human eye to detect this--we might say it was just some tone of white. But the variation in color gives clues as to what salts are there. Rayman discusses this and how the spots might have formed. Magnesium sulfate (a compound somewhat akin to "epsom salts") is considered as a likely candidate.

    Rayman also discussed the indicated presence of AMMONIA-BEARING minerals on Ceres' surface. Ammoniated clays---this was not expected and is very interesting. Also an important advantage is Ceres ever becomes a site for habitation and chemical industry.

    Things seem to be going OK. This is a great mission! The targets (especially Ceres) and the solar powered ion propulsion technology were forward looking. I was worried Dawn might not make it down to this final nearest orbit and am very glad it seems so far to be operating as planned.
     
    Last edited: Dec 31, 2015
  6. Dec 31, 2015 #806

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Besides the December 2015 Dawn Journal, we also have a new status update for 31 December:

    ==quote Rayman==
    December 31, 2015 -Dawn Busy as Year Ends

    Dawn is transmitting its latest Ceres observations, orbiting the dwarf planet while pointing its main antenna to Earth. This afternoon the spacecraft will use its ion engine to perform an orbit maintenance maneuver, which will keep its orbit matched with the plan for obtaining good coverage of the world beneath it. Following that, the probe will turn again to point its instruments at Ceres and resume collecting data.

    The December Dawn Journal describes the highest priority scientific observations Dawn is conducting in this fourth and final mapping orbit.
    ==endquote==
     
  7. Dec 31, 2015 #807

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    Uh. The human body has more weight from protons than from neutrons, and if we exclude hydrogen the difference is negligible. We are composed of 65% oxygen-16, 18% carbon-12, 10% hydrogen-1, 3% nitrogen-14, 1.4% calcium-40, 1.1% phosphorus-31 and 1.5% other isotopes.
    Of this list, phosphorus is the only isotope with more neutrons (16) than protons (15). This tiny difference has no chance against the 10% mass from hydrogen (pure protons). The 0.15% mass difference between protons and neutrons is negligible as well. Even if the 1.5% mass in the other isotopes would be pure neutrons, protons would win. Iron is the first element where the number of neutrons is significantly more (30 neutrons for 26 protons in the most frequent isotope), but its contribution to a human body is just 0.006%.
     
  8. Dec 31, 2015 #808

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I like very much the critical checking of Rayman's statement in quantitative detail.
    It inspires me to ask rather than take what he says for granted. Isn't it true though that most of the mass in an oxygen-16 atom is in the neutrons?
    Just because neutrons are very very slightly more massive than protons?
    Isn't that also true about carbon-12?
    So Rayman says:
    " neutrons constitute most of the mass of atoms other than hydrogen ... in your correspondent."

    It seems true that if you reduce the human body to atoms and sort out and remove all the hydrogen atoms---so now you have all the atoms other than hydrogen in the body---then all or at least the overwhelming majority of those atoms have at least as many neutrons as protons. And so...

    And so, by a slim majority, more than half of the mass of those atoms (other than hydrogen) IS IN FACT in the neutrons. So the neutrons constitute most of the mass of those atoms (other than hydrogen) by a very slim majority.

    Rayman was just being playful I think, in veering off into near irrelevancy, but he may in a sense have been right.
     
    Last edited: Dec 31, 2015
  9. Dec 31, 2015 #809

    OmCheeto

    User Avatar
    Gold Member

    Nucleons, Neutrons....... whatever.

    I'm wishing Dawn, Dr. Rayman, and everyone, a Happy New Year! :smile:
     
  10. Jan 1, 2016 #810

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    Ignoring the technical issues with nuclear binding energy, something like 50.1% neutrons (half of the effect from the mass difference, the other half from phosphorus) - well, technically it is more than 50%, but "most"?
     
  11. Jan 1, 2016 #811

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I certainly agree his wording ("most" of the mass) was ill-advised even if technically correct. "Most" suggests a substantial majority (at least to me and probably to most people) rather than a very slim majority like 50.1% versus 49.9%. Gives the wrong impression --- mostly a matter of nuance.
     
    Last edited: Jan 1, 2016
  12. Jan 5, 2016 #812

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    New status update from Rayman:

    ==quote==
    January 4, 2016 -Dawn Concludes a Productive New Year's Weekend

    After using its ion engine for almost 11 hours on Dec. 31 - Jan. 1 to adjust its orbit slightly, keeping it synchronized with the plan for mapping Ceres, the spacecraft resumed its observations. Since then, it has been taking more pictures and measuring spectra of infrared light and two kinds of nuclear radiation. It has also been sending a radio signal that engineers and scientists use to track its orbit in order to map the interior structure of the dwarf planet. (The radiation and orbit measurements are explained in the most recent Dawn Journal.)

    This afternoon the spacecraft will turn to point its main antenna to Earth and then spend about a day transmitting its latest results. Tomorrow afternoon it will turn once again to aim its sensors at the rocky, icy ground and collect more data until its next pause on Jan. 8
    ==endquote==

    So Dawn is pausing for transmission much more frequently now. It used to pause about once a week, in HAMO. I came to expect a pause (for some 25 hours) to happen around Thursday.
    Now apparently it paused on afternoon 4 Jan, and will resume taking data on afternoon 5 Jan.

    Rayman says the next pause will start on 8 Jan. So that suggests a pause starts every 4 days: 4 Jan, 8 Jan, 12 Jan, etc.
    That suggests that Dawn is taking data at such a high rate it fills up its memory in about 3 days of observation and then needs a day or so to send it to us.
     
    Last edited: Jan 5, 2016
  13. Jan 5, 2016 #813

    OmCheeto

    User Avatar
    Gold Member

    Did we both, really, do the math? Or did you know that off the top of your head?

    omg.nerds.pf.2016.01.05.1014.pst.png
     
  14. Jan 5, 2016 #814

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    I did the math.
     
  15. Jan 5, 2016 #815

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Bravo OM! I just took the 50.1% that Mfb mentioned. Assumed it was about right and took his word for it. You actually did the computation and tabulated the results! It's instructive for us to see a table like that---inventorying the atoms in the human body. Must have been a fair amount of work. Thanks for taking the trouble! Here's Mfb's post.
     
  16. Jan 5, 2016 #816

    OmCheeto

    User Avatar
    Gold Member

    But you didn't share the data.

    As I recall, I corrected a couple of people's math's about a year ago.
    The fact that my maths has been corrected 100 time more often, is irrelevant. o0)

    [edit]
     
    Last edited: Jan 5, 2016
  17. Jan 5, 2016 #817

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    It's nice you checked with Rayman and got a response. Still just a question of nuance which needn't interfere with our general happiness with Dawn's performance in LAMO, the new orbit.
    I see that Goldstone antenna#14 is still receiving data at 125 kilobit per second. According to Rayman that should stop sometime this afternoon (he usually talks pacific time, it's 1PM now) and the probe should resume observation.
     
  18. Jan 5, 2016 #818

    OmCheeto

    User Avatar
    Gold Member

    I've had about a thousand questions I wanted to ask, but they were mostly trivial, so I gave him a break.

    Why hasn't the MYSTIC simulator been updated since December 26th? Is it broken? Is it wrong? Has Dawn been flung off by some gravitational anomaly into deep space?
    What the hell is a gravitational quadrupole? Are there quintrupoles? What about duodecotrupoles?
    What are you going to do with yourself when the mission is over?
    Why is science so much fun?
    When are we going to see a picture of Ahuna Mons?
    Why is my breakfast getting cold?
    etc, etc, etc.......
     
  19. Jan 5, 2016 #819

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

  20. Jan 5, 2016 #820

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    As advertised the pause for data transmission that started on the afternoon of the 4th ended this afternoon (probably about 25 hours later). I checked DSN at 6pm pacific and there was just a tracking signal (10 bits per second) being monitored by Goldstone antenna#26.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted