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Near-Infrared Spectra: Specific Molecules Chad Trujillo (Gemini Observatory). Introduction Part 1: Background - Why ices and why the near-infrared? - Detections on KBOs and KBO analogues: Water, Methane, and other molecules Part 2: How to end an Easter egg hunt
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Chad Trujillo (Gemini Observatory)
Part 1: Background
- Why ices and why the near-infrared?
- Detections on KBOs and KBO analogues:
Water, Methane, and other molecules
Part 2: How to end an Easter egg hunt
- For the first time, we can count the bright KBOs
- Required signal for detection and physical interest
- List of KBOs that have been well-studied
- List of KBOs we can (reasonably) study
- Summary of population-wide spectroscopic results
correcting for signal to noise bias
There are two reasons to study KBOs:
1) Dynamics of an old (but not primordial) population
- tracer of pristine thermal history
- possible geologic effects
- sensitive to ion bombardment
- reservoir for atmosphere
- very difficult to study in other solar system populations
due to thermal alteration
- compositions can constrain models (i.e. Nice, etc.)
- very deep transitions in the near-infrared
- almost completely neutral in the visible
1998 Cruikshank et al.
2003 EL61, Orcus, Quaoar, 1996 TO66, 1999 DE9,
2002 AW197, 2002 TX300?, Charon, Phoebe, Triton
-Where signal/resolution allow, crystalline water ice
-Crystalline water ice may have a lifetime shorter
than the age of the solar system
-Transition shape is somewhat sensitive to temperature
-All have 0.1 < e < 0.2 except Quaoar (0.035) and DE9 (0.4)
-But, what is the fraction of KBOs with water, really?
can be crudely
100% water ice
and nothing else
(Trujillo et al.
2003 UB313, 2005 FY9, Sedna, Pluto, Triton
-Methane has a high vapor pressure
-It may only be present on the largest bodies
-Has been found to be pure (2003 UB313) as well
as dissolved in N2 (Pluto)
-Line position is sensitive to temperature and
-But, what is the fraction of KBOs with methane, really?
be crudely fit
with 100% pure
(Brown et al. 2005)
Ammonia hydrate: Quaoar, Charon
Cyanides: Phoebe, 2003 EL61?
Methanol: VE95, Pholus
Nitrogen: Pluto, Triton
CO: Pluto, Triton
CO2: Phoebe, Triton
-But, what is the fraction of KBOs, really?
water ice only
water ice +
This is not an
since there are
drop, which is
seen in other
bodies and may
Made a simple monte-carlo simulation of ice observations:
-Model near-infrared spectral observations comparing
science goal to control spectrum
-Assume albedo is unknown and neutral material may
be present in control spectrum
-Simulated H and K, but found that signal requirements
are similar for both.
-Want to determine the required signal-to-noise
ratios (S/N) for detection / non-detection
-Relate this to S/N achievable at large (8m – 10m)
to 10% for
to 10% for
40 water/methane detection
80 xwater detection
200 methanol/ammonia detection
200 water/methane fraction to 10%
500 water/methane temp, N2/CO/CO2/Ethane limits
water: 7/16 EL61,Q.,O.,AW197,DE9,TO66,TX300
methane: 3/15 FY9,UB313,Sedna
xwater: 4/4 EL61,Q.,O.,TO66,AW197?,DE9?
mthnl/NH3: 2/4 Q.=NH3:H2O,VE95=methanol
Ethane: 1/1 FY9
No CH4/H2O: 6/15 CS29,TL66,GN171,WR106,Huya,Ixion
Pluto: Methane, N2, CO, Ethane?
Charon: xwater, NH3, NH3:H2O
Triton: Methane, N2, CO, CO2, 13CO
Phoebe: xwater, CO2, OH, CH, CN, Fe2+, metal-OH, phyllosilicate
Combining all our resources in an international
collaboration, we can probably get about
15 nights / year of 8m – 10m telescope time
~ 70 hours / year of integration time
~ 200 hours over next 3 years
Much more time than this is wasted every year
outside the solar system.
S/N~100 in 1 hour for a K=18 object
What can we do?
About 4 of
of these have
The Good News:
- There are about 40 KBOs left that could use 8 hours
of exposure time, 8 of which could use 1 hour for marginal results
- About 25 KBOs could be observed by an international
team of collaborators using the world's largest
- Such an effort would produce ~8 X/H2O detections,
~5 CH4 detections, a few temperatures, a few good
N2/CO limits, tripling our knowledge of KBO surfaces
The Bad News:
- Don't bother observing any of the brightest 15 KBOs
unless you spend at least 4 hours of exposure time
on a 8m – 10m telescope in good conditions.
After taking into account S/N issues:
-100% (4) of water ice is crystalline
-44% (7/16) of KBOs show water ice
-50% (2/4) of KBOs show ammonia hydrate or methanol
-20% (3/15) of KBOs show methane ice
-Only the biggest KBOs have methane ice, is this
physical or small number statistics?
-Only 1 KBO has been observed deeply enough to
detect N2/CO/CO2/Ethane (FY9, Ethane only)
-40% (6/15) of KBOs are featureless
-No clear correlation between surface and orbital parameters
-Results are similar with inclusion of KBO analogues (Pluto,Charon,etc.)
Tips for observers:
-Don't repeat objects that are already done!
-Observe in good conditions and at low airmass!
-Take high (80-100) S/N spectra!