The Astonishing Redness of Kuiper-Belt Objects, by = Wickramasinghe and Hoyle

COSMIC=20 ANCESTRY | Quick=20 Guide | Next | Feedback | All = Rights=20 Reserved

*** Cosmic Ancestry = preprint of=20 Astrophysics and Space Science v 268 p 369-372, 1999=20 ***

THE ASTONISHING REDNESS OF
KUIPER-BELT OBJECTS What'sNEW

by=20 N.C. Wickramasinghe and F. Hoyle
School of Mathematics, Cardiff = University
PO Box 926, Senghennydd Road
Cardiff CF2 4YH, UK=20
E-mail: wickramasinghe@cf.ac.uk

Abstract:The recently reported extreme redness of a = class of=20 Kuiper-belt objects could be yet another indirect indication of=20 extraterrestrial microbiology in the outer solar system.=20

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Look not thou upon the wine when it is red, when it giveth = his=20 colour in the cup,=85
At the last it biteth like a serpent, and = stingeth=20 like an adder. =97 Proverbs, xxiii. = 31
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The existence of an ancient reservoir of cometary-type objects = in=20 stable circular orbits lying beyond the orbit of Neptune is now = beyond=20 dispute. Tegler and Romanishen (1998) have recently made the = remarkable=20 discovery that these so-called Kuiper-belt objects include some = that are=20 exceedingly red. Accurate photometic studies using CCD techniques = have=20 revealed two distinct classes of such objects. One class is = comprised of=20 objects with surface colours that are only very slightly redder = than the=20 sun, whilst the other contains objects that are said to be "the = reddest=20 objects of the Solar System". The fact that the distribution of = colour=20 amongst these objects does not correlate with heliocentric = distance=20 indicates that the intensity of solar radiation does not = play an=20 important role in the colouring process.=20

The so-called reddest objects have a B-V colour excess relative = to the=20 Sun typically of ~ 0.65 mag, and a V-R = colour=20 excess of ~ 0.4. This implies that the = ratio of=20 reflectivity at the wavelengths 4500A and 6500A is=20

f =3D R(6500A)/R(4500A) =BB 2.5 (1)=20

Table 1 compares this value with reflectiviy ratios extracted = from the=20 data of Tholen et al. (1986) for a representative set of = comets and=20 D-type asteroids. From Table 1 we see that the surfaces of comets = and=20 asteroids fall significantly short of meeting the condition = implied by=20 (1). Table 2 sets out experimentally determined values of the same = ratio f=20 for several different types of laboratory materials (CRC=20 Handbook of Chemistry and Physics, 54^th ed., = 1973;=20 Larson and Fink, 1977). We note from here that some mineral = surfaces could come close to satisfying (1), but by far the best=20 candidates for producing redness are naturally occuring pigments = as=20 typified by the data for 'ripe pear' and 'ripe peach'.=20

Table 2 also includes data for irradiated hydrocarbon mixtures=20 (Andronico et al., 1987). The relevant values of f range = from 3.3=20 to 1, decreasing with increasing radiation dose = beyond a=20 certain point. Generally similar results are reported for = irradiation with=20 high-energy photons rather than nucleons. In all cases colours = ranging=20 from 'yellow' to 'brown' can be generated under carefully = controlled=20 conditions, and with precisely chosen cut-off values of radiation = doses.=20 On the basis of such laboratory data one could thus conclude that=20 prolonged exposure to high-energy radiation, as occurs in = interplanetary=20 space, would lead eventually to the appearance of a grey or = neutral=20 colour. One might try to retrieve the case for radiation colouring = by=20 invoking meteorite and micrometeorite impacts. Such impacts, it = could be=20 said, arrests this greying process by continually exposing a = pristine=20 cometary surface that will be subject only to brief interludes of=20 irradiation. But it is clear from Table 1 that the colours of real = comets=20 exposed to the interplanetary environment do not bear testimony to = such an=20 effect. Indeed Halley's comet and other long-period comets that = spend most=20 of their time in the outer regions of the solar system have mostly = neutral=20 colours, whilst the shortest period comets show reddening, albeit = to a=20 minor degree. From Table 2 it is clear that the reflectivity ratio = given=20 by (1) is consistent with the presence of highly absorptive = organic=20 chromophores (pigments) that have their absorption peaks = distributed over=20 green to red wavelengths.=20

Table 1

Reflectivity ratios for comets and asteroids =

Object

Reflectivity Ratio,=20
R(6500A)/R(4500A)

Comets, period < 20 yr

1.26

Comets, period > 35 yr

1.11

P/Halley (Period 76yr)

1.00

D-type Asteroids(Mean)

1.16

Kuiper-Belt Red Class

2.50

Table 2

Reflectivity ratio, f , for laboratory systems =

Laboratory system	Reflectivity Ratio, R(6500A)/R(4500A)=20
Pyroxene	1.58
Olivine	1.63
Ripe pear	3.67
Ripe peach	4.15
Irradiated organics	3.30 decreasing with dose to=20 1.0

=20

For many years the present authors have maintained that red = colorations=20 of planetary ices, for example the surface of Europa, could most = plausibly=20 be explained on the basis of biological pigments (Hoyle and=20 Wickramasinghe, 1983, 1997; Hoover et al., 1986). Such = pigments=20 will be continually regenerated and brought up to the surface as = long a=20 biological activity persists. Suitable candidates for such = pigmented=20 microorganisms could be found among the Antarctic snow-ice algae=20 Chlamydomonas, and diatoms. These organisms, which produce = brownish=20 and reddish colorations throughout the polar regions, might well = serve as=20 an analogue for the colours of icy bodies in the Kuiper belt. It = may be=20 relevant in the present context that diatoms are able to replicate = and to=20 carry out photosynthesis beneath an ice crust, operating at light = levels=20 of less than 1% that at the surface (Hoover et al., 1986).=20

We have argued elsewhere that radioactive heat sources present = in=20 primordial solar material would inevitably produce melting of ices = in the=20 interiors of comets (Hoyle and Wickramasinghe, 1983; Wallis and=20 Wickramasinghe, 1992). The larger objects amongst the comets, = giant comets=20 with radii greater than, say 50km, may also be appropriate = representations=20 of Kuiper-belt objects. Such objects could retain interior lakes = beneath=20 an ice crust for timescales that may even exceed the age of the = solar=20 system. Anaerobic bacterial activity in subsurface lakes, leading = to the=20 build-up of high-pressure gas pockets, could cause sporadic = cracking of an=20 overlying ice layer. And this in turn leads to the transport of = biological=20 pigments to the surface.=20

The classes of red and grey Kuiper-belt objects discovered by = Tegler=20 and Romanishen could thus mark out a simple distinction between = objects=20 that are biologically active from those that are not. In objects = where=20 biological activity has ceased the red pigments would rapidly = degrade to=20 become grey.

What'sNEW

2000,=20 October 25: Red and grey Kuiper-belt objects have different = orbits.

2000,=20 January 5: The spectrum of Pluto's moon, Charon, shows crystalline = ice.=20
1998, March 21: Two distinct classes of = Kuiper-belt objects=20 -- the story that promped this article.=20

References

Andronico, G., Baratta, G.A., Spinella, F. and = Strazzulla, G.:=20 1987, Astonon.Astrophys 184, 49-51=20

CRC Handbook of Chemistry and Physics, 54th ed: = CRC=20 Press, 1973

Hoover, R. B., Hoyle, F., Wickramasinghe, N. C., = Hoover, M. J.=20 & Al-Mufti, S.: 1986, Earth, Moon, and Planets, = 35,=20 19-45

Hoyle, F. and Wickramasinghe, N. C.: 1983, Living=20 Comets, Univ Coll. Cardiff Press

Hoyle, F. and Wickramasinghe, N. C.: 1997, Life on = Mars? The=20 case for a cosmic heritage Clinical Press, Bristol

Larson, H.P. and Fink, U.: 1977, Applied = Spectroscopy,=20 31, 386

Tegler, S. and Romanishin, W.: 1998, Nature, = 392,=20 49-51

Tholen, D. J, Cruikshank, D. P, Hartman, W. K, Lark, N, = Hammel,=20 H. B. & Piscitelli, J. R.: 1986, Proc. 20th ESLAB Symposium = on the=20 Exploration of Halley's Comet, Heidelberg 27-31 October 1986, = ESA=20 SP-250, Vol . III, 503-507=20

Wallis, M.K. and Wickramasinghe, N.C.: The = Observatory,=20 112, 228-234=20

Acknowledgement

This work was supported by a grant from = Acorn=20 Enterprises LLC, Memphis, TN.

COSMIC=20 ANCESTRY | Quick=20 Guide | Next | Feedback | All = Rights=20 = Reserved

THE ASTONISHING REDNESS OFKUIPER-BELT OBJECTS What'sNEW

What'sNEW

References

Acknowledgement

THE ASTONISHING REDNESS OF
KUIPER-BELT OBJECTS What'sNEW