Download MIRS - A Map of the Ice Regions in the Solar System J. Agarwal1, T

MIRS - A Map of the Ice Regions in the Solar System
J. Agarwal1, T. Albin1, H. Böhnhardt1, B. Dabrowski1, M. Fränz1, N. Kappelmann3, H. Krüger1, P. Lacerda1,
U. Mall1, S. Mardaneh2, N. Oklay1, R. Orlik1, E. Roussos1, C. Snodgrass1, R. Srama2, C. Tubiana1,
J.-B. Vincent1, K. Werner3
1) Max-Planck Institute for Solar System Research, Göttingen, Germany
2) Institut für Raumfahrtsysteme, University of Stuttgart, Stuttgart, Germany
3) Institute for Astronomy and Astrophysics, University of Tübingen, Tübingen, Germany
Proposal
We propose a low-cost mission that will allow mapping the distribution of icy objects in the Solar System
in order to constrain solar system evolution models.
Scientific Rationale
Eccentricity
Recent theoretical progress has led to the development
of a scenario for the dynamical evolution of the Solar
System, which explains essential features of the planetary system in which we live. The Nice model proposes
the migration of the giant planets from an initial, more
compact configuration into their present positions, long
after the dissipation of the initial proto-planetary gas disk.
0.4
0.3
0.2
0.1
0
0.4
0.3
0.2
0.1
0
0.4
0.3
0.2
0.1
0
0.4
0.3
0.2
0.1
0
0.4
0.3
0.2
0.1
0
0.4 150 Myr
0.3
0.2
0.1
0
0 kyr
70 kyr
100 kyr
300 kyr
500 kyr
600 kyr
2
4
6
8
10
Semimajor axis (AU)
Figure:
Theevolution
evolution
of the small-body
populations
Figure 2 | The
of the small-body
populations during
the growth
and migration of the giant planets, as described in Fig. 1. Jupiter, Saturn,
during
the growth and migration of the giant planets.
Uranus and Neptune are represented by large black filled circles with evident
inward-then-outward
migration, and
Saturn,circles
Uranus and
Planets
are represented
by evident
large growth
blackoffilled
with
Neptune. S-type planetesimals are represented by red dots, initially located
evident
inward-then-outward migration. S-type planbetween 0.3 and 3.0 AU. Planetary embryos are represented by large open circles
(butrepresented
not in scale relative
planets),
where Mlocated
is mass.
scaled by M1/3are
etesimals
byto the
redgiant
dots,
initially
The C-type planetesimals starting between the giant planets are shown as light
between
0.3theand
3.0 planetesimals
AU. Planetary
embryos
arebetween
repreblue dots, and
outer-disk
as dark blue
dots, initially
. For allopen
planetesimals,
filledFigure
dots are used
if they
are inside
8.0 and 13.0
sented
byAUlarge
circles.
from
Walsh
ettheal.,
Key Goals
be done with the Hubble Space Telescope, for example)
We propose here a low cost mission to place a has the advantage of much greater sensitivity. The outdedicated platform into a fast reachable orbit (e.g.
inclined orbit, or Lagrangian point) which can
operate for a long duration period with the goal to:
• identify signatures of water and volatiles in mainbelt asteroids, Near-Earth Objects (NEOs) and distant objects (Centaurs, Kuiper belt objects and
the moons of giant planets) with the goal of mapping the distribution of water in the solar system;
• identify and characterise Main Belt Comets (MBCs)
and bodies like Themis, Ceres and others - the most
likely candidates to hold water ice LETTER
among the
asteroids;
RESEARCH
• observations of UV emission of the exospheres of the
terrestrial
observations
of aurorae
of8.0
outer
planets;
and
the C typesplanets,
from between
the giant planets
and from
to 13.0
AU.
The
consists of more
and C-type
• present-day
extend asteroid
our beltpicture
of than
thejust S-NEO
popasteroids, but this diversity is expected to result from compositional
ulationwithin each
andparent identify
potentialInformation).
hazards.
gradients
population (Supplementary
There is a correlation between the initial and final locations of
implanted asteroids (Fig. 3a). Thus, S-type objects dominate in the
inner
belt,near-infrared
while C-type objects
dominate
in the outer belt
3b).deWhile
(NIR)
spectroscopy
is a(Fig.
well
Both types of asteroid share similar distributions of eccentricity and
veloped(Fig.
and3c,proven
methodasteroid
to identify
ices (of
water,
inclination
d). The present-day
belt is expected
to have
had
its eccentricities
and inclinations
reshuffled on
during
so-called of
methane
or other
volatile
species)
thethesurfaces
13,14
late heavy bombardment (LHB) ; the final orbital distribution in our
our targets, it is applicable only to the brightest bodies
simulations matches the conditions required by LHB models.
(even
when
using
the oflargest
modern
telescopes
from
Given the
overall
efficiency
implantation
of ,0.07%,
our model
{3
M+ of
S-type asteroids
at the time
of the dissipation
yields
*1:3|10
Earth)
and is not
suitable
to identify
water
released at
of the solar nebula. In the subsequent 4.5 Gyr, this population will be
lower by
rate
(< 1E26
molecules/s)
from
by a asteroids
further factorin
of its
depleted
50–90%
during the
LHB event13,14 and
15
. The in
present-day
asteroid
belt be
is estimated
,2–3
by chaoticSince
diffusion
gas phase.
water
asteroids
must
buriedtobe12
{4
M
,
of
which
1/4
is
S-type
and
3/4
is
C-type
.
have
a
mass
of
6|10
+
low the surface to have survived to the present day,
Thus our result is consistent within a factor of a few with the S-type
NIR spectroscopy
portion
of the asteroid belt.is of limited use for constraining the
The C-typeof
share
of the asteroid
belt is determined
by the total mass
presence
water,
even ignoring
the sensitivity
limits
of planetesimals between the giant planets and between 8 and 13 AU,
of current technology. Therefore, water must be dewhich are not known a priori. Requiring that the mass of implanted
tectedmaterial
via emission
from
gas phase,
following
C-type
be three lines
times that
of the
the S-type,
and given
the
implantation
efficiencies
reported
this implies
following
its sublimation
from
theabove,
subsurface
ofthat
thethesmall
body.
Identification Technique
gassing rates of MBCs and other water bearing asteroids
are very low, but a dedicated imaging system allows integration across the whole OH band and the whole area
of the diffuse OH coma, and integrations on each target
over many hours and days. In such a way a small, cheap
mission can achieve greater sensitivity than is possible
using more expensive but a general-purpose space observatory, and achieve a very significant result: A map of
the location of present-day water ice in our solar system.
Instrumentation and Mission Design
i (°)
Relative number
First photometric calculations indicate that a telecope
with a 30 cm mirror and a mass <20 kg could be sufficient to detect potential water gas phases around asteroids using simple nonimaging spectrometers.
e
8
Number
As
water can be best detected via its daughter molecules,
a 50
t = 0its
yr existence
primarily
the OH radical, one can identify
40
t = 100,000 yr
via30photometry and/or spectroscopy covering
t = 600,000the
yr UV
20 around the 308nm OH emission line. This line is
range
10
the 0strongest seen in comet spectra, but is challenging
0
2
4
6
10
b
to observe
from
the ground
due
to UV 8absorption
by
1
main asteroid belt and smaller open dots otherwise. The approximate
Inner disk
ozone
atmosphere and has only been ob0.8 in the terrestrial
boundaries of the main belt are drawn with dashed curves. The bottom panel
Trans-Neptunian disk
0.6
combines
the
end
state
of
the
giant
planet
migration
simulation
(including
only
served
from
the
ground
Inter-planet
disk in bright, highly active comets.
Despite reproducing several major events in the evo0.4
those planetesimals that finish in the asteroid belt) with the results of
0.2
lution
of ofthe
System
(e.g. axis
thea ,Late
Heavy
Bomsimulations
innerSolar
disk material
(semimajor
2) evolved
for 150
Myr
.
(see Fig. 4), reproducing
successful
terrestrial
planet
simulations
bardment
of the inner
planets,
and
the
formation
of the c 0
30
Oort
cloud) the Nice model remains unsatisfactory. Due
20
and planetesimals (small), while the planetesimal population exterior
toto the
model’s
manybetween
free parameters,
wide
Jupiter
is partitioned
inter-planetary abelts
andrange
a trans-of
10
Neptunian disk
(8–13 AU). are
The planetesimals
from themaking
inner disktestare
dynamical
outcomes
feasible, thereby
0
d
considered to be ‘S type’ and those from the outer regions ‘C type’. The
able
predictions
observationally
difficultplanetesimals
to constrain.
0.4
computation
of gas drag
assumes 100-km-diameter
and
Earlier,
more
of the
evolution
uses a radial
gasstatic
densitytheoretical
profile taken models
directly from
hydrodynamic
0.2
4
simulations
(see
Supplementary
Information
for
details).
of the solar system relied on the concept of a snow line
0
The inward migration of the giant planets shepherds much of the
1
2
3
asS-type
a more
or inward
less fixed
heliocentric
the somaterial
by resonant
trapping, distance
eccentricityin
excitation
Semimajor axis (AU)
doubles, reaching
andnebula
gas drag.separating
The mass of two
the disk
inside 1 AUdistinct
lar
physically
regions:
*2M+ . This reshaped inner disk constitutes the initial condition Figure 3 | Distributions of 100-km planetesimals at the end of giant planet
afor
central
region where the environment is too hot for
a, The semimajor axis distribution for the bodies of the inner disk
terrestrial planet formation. However, a fraction of the inner disk migration.
Figure:
Orbit
ofasteroid
asteroid
Oljato
exemplifying
how the
that
are
implanted
in
the
belt
are
plotted
at
three
times:
the
beginning
light
element
(HCNO)
compounds
to condense
andthe
the
(,14%)
is scattered
outward,
ending up beyond
3 AU. During
ofJPL
the simulation
(dotteddata
histogram),
the end
of inward
planet migration
small body
baseat was
used
to find
suitable assubsequent
outward
migration
of
the
giant
planets,
this
scattered
disk
solid phase consists mainly of rocky material, and a more (dashed) and at the end of outward migration (solid). There is a tendency for
teroids
whichtocould
be tracked
with alocation.
30 cm
telescope
of S-type material is encountered again. Of this material, a small frac- S-type
planetesimals
be implanted
near their original
Thus,
the
distant
one
where
solid
ice
grains
can
readily
form.
The
tion (,0.5%) is scattered inward and left decoupled from Jupiter in the outer
edge
their final distribution
related tobetween
the original 2014
outer edge
of the
from
L2of during
a missionis flown
and
2020.
idea
of belt
a snow
clearaway.
predictions
for where
asteroid
regionline
as theleads
planetsto
migrate
The giant planets
then S-type disk, which in turn is related to the initial location of Jupiter. b, The final
The visibility
ofS-type
the asteroid
is show
in the next
figure.
numbers of the
(red histogram),
the inter-planet
population
encounter
material
thesolar
Jupiter–Neptune
formation
region,planesome relative
ice
can bethe
found
ininthe
system. Even
though
of which (,0.5%) is also scattered into the asteroid belt. Finally, the (light blue) and the outer-disk (dark blue) planetesimals that are implanted in
tary
induces
significant
of the various
asteroid
belt are shown
as a function
semimajor axis.
orbital
The
detection
of very
weakof activity,
as The
is expected
for
giantmigration
planets encounter
the disk
of materialmixing
beyond Neptune
(within the
(c) and eccentricity (d) are plotted as a function of semimajor axis,
13 AU) of which only
,0.025% reaches
a finalatorbit
in the asteroid
belt. inclination
planetesimal
populations
formed
different
temperaMBCs
and
other
weakly
objects,
with the same symbols
used
in Fig. 2. active
The dotted
lines showrequires
the extent ofan
theunWhenthe
the giant
planets have
their migration,
the asteroid
belt asteroid belt region for both inclination and eccentricity, and the dashed lines
ture,
ice content
offinished
an object
is a strong
indicator
realistic amount of ground-based observing time, even
population is in place, whereas the terrestrial planets require an addi- show
the limits for perihelion less than 1.0 (left line) and 1.5 (right line). Most of
oftional
its formation
location,
is largely preserved over the
,30 Myr to complete
theirand
accretion.
onouter-disk
the largest
or orbits
observations
from while
outside
materialtelescopes,
on planet-crossing
has high eccentricity,
asteroidofbelt
implanted
the simulations
is composed
the objects
from between theThe
giant latter
planets were
scattered earlier
theThe
history
our
Solar inSystem.
This fact
offers ofa two
way many
the ofEarth’s
atmosphere.
approach
has and
many
separate populations: the S-type bodies originally from within 3.0 AU, therefore damped to lower-eccentricity planet-crossing orbits.
to use the current surviving and observable planetesi- advantages, and a dedicated search needs only a small
1 4 J U LY 2 0 1 1 | VO L 4 7 5 | N AT U R E | 2 0 7
mals as tracers for the evolutionary processes in which telescope (30-50cm
aperture) with fast optics and a nar©2011 Macmillan Publishers Limited. All rights reserved
they were involved. In this context, it is inherently rowband filter to image at 308nm to perform a high efclear that the strongest tracer of the origin and history ficiency survey. A survey using photometric detection
of a body in the Solar System is its water-ice content. of OH (rather than high resolution spectroscopy, as can
Figure: Visibility of sample asteroid Oljato as seen
from L2 during time frame 2014-2020.
Figure: Telescope design used to study the feasibility of
the mass payload assumptions.
For an envioned payload which could carry additional instruments beyond the telescope, three types of
launcher are feasible: Long March (CZ2), Soyuz/Fregat
and Vega. The Long March launcher could transport a
mass of up to 1400 kg to GTO.
Reference: Walsh, K., Morbidelli1, A., Raymond, S.N.,
O’Brien, D. & Mandell, A., A low mass for Mars from
Jupiter’s early gas-driven migration, NATURE, Vol. 475,
206-209, 2011.
Interested parties please contact:
Urs Mall (email: [email protected])
Max-Planck Institute for Solar System Research
Göttingen, Germany