europa - deeps · europa, the size of our moon, is thought to have a crust of ice perhaps 100 km...

Europa

Overview 2

1. Evidence for an Ocean?

2. Surface Features & Composition

3. Energy & Prospects for Life

Europa! 3

The color image of Europa on the right was acquired by Voyager 2.Europa, the size of our Moon, is thought to have a crust of ice perhaps 100 km thick.

The relative absence of features and low topography suggests the crust is young and warm a few kilometers below the surface. The tidal heating process suggested for Io also may be heating Europa's interior at a lower rate.

The complex array of streaks indicate that the crust has been fractured and filled by materials from the interior. The lack of relief and any visible mountains or craters on its bright limb is consistent with a thick ice crust.

Europa! 4

‘True’ Color ‘Enhanced’ Color

The surface of Europa is dominated by water ice.

In the false-color image on the right, coarse-grained ice is dark blue (near poles) and finer-grained ice is lighter blue; reddish/brown tones indicate a non-ice component.

The linear features that streak across the surface are believed to result from warm ice/water coming to the surface during extension/fracturing of the crust.

Parent Child

(0.4) (0.67)

Liquid Ocean on Europa? 8

Why do we think that Europa may have a liquid ocean?

However, it is possible that Europa is instead dominated by a thick ice mantle that experiences convection, with only a thinner layer of liquid. What would this imply for the search for life on Europa?

Gravity measurements & magnetometer data!

- we can measure the gravitational effects/moment of inertia of the body to determine if some part of the interior is liquid

- the presence of an induced magnetic field; this means that there must be an electrically conductive material inside Europa that generates a magnetic field when it interacts with Jupiter’s magnetic field; this could be due to a salty liquid ocean

No Clear Answer.....Yet 9

Is the surface a relic of past activity during a ‘thin shell’ epoch or are the ‘thin shell’ features being formed today?

Constraints from gravity data10

Moment of inertia coefficient (I = CMR2): C = 0.346 +/-0.005, Bulk density: 3018 +/-35 kg m-3

(415 km) Core: Fe or FeS, 8000 kg m-3

(1425 km) Mantle: Silicates, 3000 kg m-3

(1560 km) Hydrosphere: Water , 1000 kg m-3

3-layer model 5-layer model

(234 km) Inner Core: Fe, 8000 kg m-3

(624 km) Outer core: FeS, 7300 kg m-3

(1451 km) Mantle: Silicates, 3150 kg m-3

(1513 km) Lithosphere: Hydrates, 1300 kg m-3

(1560 km) Hydrosphere: Water , 1000 kg m-3

C = 0.3465 Bulk density = 3002 kg m-3

C = 0.3429Bulk density = 3030 kg m-3

Ice/Ocean: 135 km thick Ice/Ocean: 47 km thick

Water Plumes on Europa? (UV observations) 11

Europa: Surface Features 12

Global Map of Europa

The surface of Europa lacks impact craters(indeed, there is only one putative impact crater that has been identified!)

The surface of Europa is very young, possibly 10s of millions of years old, but likely no more than several 100s of millions of years old.


Again, we can use cross-cutting relationships to determine relative surface ages.


This double ridge is one of the youngest features on Europa.


Chaotic, fracturedterrain on Europa

Europa: Surface Composition 19

Kuiper (1957 AAS Meeting)

The presence of ices and other non-silicate (non rocky) materials on the Galilean satellites has been known for many decades.

More recently, of course, we have sent spacecraft to this part of the solar system to examine these bodies in great detail, and missions like Galileo carried NIR spectrometers along.

This information was primarily from visible-near infrared reflectance data (VIS-NIR spectroscopy) of the surface using ground-based telescopes.


McCord et al. 2002 Dalton et al. 2003

The near-infrared mapping spectrometer (NIMS) instrument on the Galileo mission provided valuable information on the surface composition of Europa.

The surface contains significant amounts of water ice and lesser amounts of other phases (e.g, sulfate salts, S-bearing acids, etc.).

Some of the apparent salt-rich regions may result from the crust pulling apart and liquid brines coming to the surface. This would form new ice-rich crust with salts, but it has not been proven to be the source of such deposits.


Carlson et al. 2009

The Galileo mission provided a much more detailed look at Europa and we have since learned that the surface composition is quite complex.

This is a huge step forward from the Voyager observations, but additional data/observations are required to sort out the details and assess the potential for life on Europa.

It is still debated whether or not the surface contains sulfate salts or acids (in addition to water ice), but the reality is that both are likely present.


Hydrated sulfates:

XSO4•nH2O

‘X’ represents the cation,but what is the cation?

Mg? Na? Ca? Other?

Is the sulfate exogenous or endogenous?

Some of the apparent sulfate saltsare associated with ‘young’ fractures/cracks (see red regions in insets to the left)....is this because they come to the surface from the salty ‘ocean’ below?

Does this imply that more of the material is endogenous?


Carlson et al. 2009

However, many regions that are apparently sulfate-rich are not associated with fractures!

In the above image (left), the reddish sulfate-bearing spots are not aligned with the fractures.


Instead, many fractures are associated with water ice (pink regions in image to the right).

Carlson et al. 2009


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Microns 3 4 5 6 7 8 9 10

“...below 3 µm, is where many overtone and combination bands dominate, and is usually ignored in the organic literature. However, many features important to those who study Earth and planetary spectroscopy can be identified here...From 3 to 8 µm is the ‘functional group’ region where absorptions due to bending and stretching of such common structural groups as –CH3, –CH2–, –C=O, N-H2, C=C,C=N,C≡C, and C≡N occur.” from Clark et al. (2009)

In the search for organic material (life?) on Europa, we need to be careful about which instruments we choose for orbiters or landers.

The ice, sulfate salt, and sulfuric acid signatures are often very strong and can overlap with or mask organic absorption features. If we want to use spectroscopy, we may want to focus on wavelengths beyond the near-infrared and instead use the mid-infrared.

Planetary Energy Budgets 26

Sources of Energy 27

The energy associated with a planet can be estimated from its luminosity, which has both external and internal sources.

The external source is primarily the energy from the Sun.

The internal energy (intrinsic energy) can come from a variety of sources.

Reflectedsolar

Thermalsolar

IntrinsicExternal

Sources of Intrinsic Energy 28

• Release of gravitational energy

• Loss of heat from initial components

• Release of nuclear binding energy through nuclear fusion

• Release of nuclear binding energy through radioactive decay

• Tidal and rotational dissipation of kinetic energy

• Ohmic dissipation of electrical currents

Tidal Energy 29

Europa is roughly the same size as the Moon, and of course the presence of the Moon is observed on Earth by changes in the ocean tides.

Tidal Energy 30

By comparison, the enormous mass of Jupiter treats Europa like the Moon treats the oceans on Earth.

Tidal squeezing causes Europa to flex, which produces internal friction, which generates heat.

Does Europa Have the Right Stuff? 31

Artistic conception of ‘life’ on EuropaWater: the subsurface ocean, possibly with salts

Energy: redox reactions; the radiation from Jupiter’s magnetosphere breaks down H2O ice to release oxygen; the ocean could contain reductants

Elements: CHNOPS could be released from vents near the rock-ice boundary at the bottom of the ‘ocean’ or from water-rock interaction

Preservation Beyond Earth 32

Just as preservation of organic material is tricky on Earth, it is also tricky on other planets/moons.

Even if the rocks/ice are preserved for billions of years, the harsh radiation environment of space can destroy organic material over time.

Life Detection on Europa 33

Life detection is tricky business....how do you separate biosignatures from abiotic organics?

Biomarker: An organic compound in natural materials (e.g., sediment, rock, water, soil, fossils, oil, etc.) that is unambiguously linked to specific precursor molecules made by living organisms.

On the surface of icy and radiation prone places like Europa, we need to consider:

- irradiated life forms - irradiated endogenous organic material (abiotic) - irradiated exogenous organic material (abiotic) - synthesis of organic material radiolytically

Liquid Ocean on Europa? 34

If Europa does have a liquid ocean, does it have life? How would we explore such an ocean?

http://www.jpl.nasa.gov/missions/europa-mission/

The Next Steps in Exploring Europa:



europa - deeps · europa, the size of our moon, is thought to have a crust of ice perhaps 100 km...

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