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M.A.D.A.N.A.C Ph. Bendjoya L.U.A.N-U.N.S/C.N.R.S

A. Cellino Osservatorio di Torino I.N.A.F

M.A.D.A.N.A.CMeasurement And Discovery of Asteroids and NEOs in

AntarctiCa



Physical characterization is losing the race against discovery

(Data from Tedesco, private communication)



Near-Earth Objects: What We Would Like To Know Better

• Inventory and Size Distribution

• Asteroidal/Cometary Contribution

• Origin, History and Evolution

• Composition

• Internal Structure: Density, Impact Strength, Macroscopic Porosity

• Regolith Properties

• Spin rates

• Binarity



How to improve our knowledge on:

• Masses and densities?

• Internal structures?

• How many?

• Size and albedo distribution?

• Taxonomic distribution?

In situ Exploration

In situ Exploration

Remote Observations

Remote Observations

Remote Observations

Statement from the conclusions of the Erice Space Chemistry School, July 2001 on “The Physical Properties of Potential Earth Impactors: Know

Your Enemy”

• The most crucial datum needed for assessing the NEO hazard is the size of the objects. This information is lacking for the majority of known NEOs and is the highest measurement priority after discovery and orbit determination.



PHOTOMETRY


A. Cellino Osservatorio di Torino I.N.A.FThermal RadiometryAsteroids emit both scattered sunlight at visible wavelengths, and thermal radiation in the IR.

Simultaneous measurement of V and thermal IR fluxes lead to determination of albedo and size. (Courtesy of S. Price)

NEOs are bright in the thermal IR !



THE (923) HERLUGA FIELD IN THE VISIBLE AND IR (MSX Observations)

(Courtesy of S. Price)



For D = 1 km

and pV= 0.16

(Computations by E.F. Tedesco)

Microns

12

8.5

4.7

0.55



Diameter in Km as a function of albedo (visible))

1 UA



(data from E.F. Tedesco)



Advantages of mid-IR observations of NEOs

Most of the available IR data have been obtained so far by space missions (IRAS,

MSX)

… but from the ground, in recent years, no more than 10 NEOs per year on the average have been observed in the thermal IR.

• Radiometry allows to obtain sizes and albedos

• Objects are bright at mid-IR wavelengths

• Stellar background substantially reduced, even at low galactic latitudes

• Modest dependence of IR luminosity on phase angle

• Radiometry allows to obtain sizes and albedos

• Objects are bright at mid-IR wavelengths

• Stellar background substantially reduced, even at low galactic latitudes

• Modest dependence of IR luminosity on phase angle

Jon Lawrence and Michael Burton



POLARIMETRY



Polarimetry

This technique is based on some empirical relationships between the degree of linear polarization (measured through the Stokes parameters Q and U) and the surface albedo.

What is usually measured is the parameter:

Pr = ( I- I ) / ( I + I//)

Where I and I are the intensities of the components linearly

polarized along the directions perpendicular and parallel to the scattering plane, respectively.



Polarization curve of 1 Ceres



The slope – albedo relationship

(from Dollfus et al., 1989)



Polarimetry in IR : never done at this moment

Inputs to models

A new way to classify taxonomy ?



SPECTROSCOPY



Asteroid Taxonomic Classes

(from Tholen and Barucci, 1989)



a): Ni-Fe

b): Olivine

c): Ortopyroxene

d): Feldspar

e): Spinel



IR spectroscopy (or color-photometry) allows to discriminate taxonomic types



DETECTION



Solar elongations vs. Earth distanceSolar elongations vs. Earth distance

Large dots: Mv < 16

Medium dots: 16 < Mv < 18

Small dots: 18 < Mv < 20

Orbital evolution of 21 Atens (821 yrs). Solar elongations vs. Earth distance every 40 days.

Aten objects: a < 1, Q > 0.983 AU

(integrations made by Boattini and Carusi)



IEOs: a class of NEOs totally interior to the

Earth’s orbit

These objects are extremely hard to discover, due to the difficulty of observing them from ground, since they never are visible at large solar elongations. The first IEO discovery has been made by LINEAR not earlier than 2003.

In addition to Atens, a new class of objects, with orbits completely inside Earth’s orbit, have been found to exist necessarily, through numerical integrations of NEO orbits performed in 2000. These objects have been called IEOs (objects Interior to Earth’s Orbit).

Where on earth can

we make observations

in direction of the sun …?



Measurements:

albedo, size, taxonomy: photometry, spectroscopy, polarimetry

M.A.D.A.N.A.C could (should ?) exist….

There are things to do at Dome C for asteroids:

Discoveries : NEOs, IEOS but also MBAs and TNOs

Great benefits of IR

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