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VIEWS George Cole Could there be life on exoplanets? Two very interesting articles in the December issue, “The astrochemistry of life” (Richards and Sarre A&G 42 6.17) and “Solar evolution and the distant future of the Earth” (Schröder, Smith and Apps A&G 42 6.26), together raise several important questions. The discovery of planetary companions of some solar-type stars suggests that some of these so-called exoplanets may carry living materials and, especially, technologically capable life. Can any indications be inferred from the present knowledge of these systems? Living materials as we know them require liquid water and a constant, moderate source of heat. For the Sun, this restricts the habitable zone for advanced life to an orbital band within about 0.7 and 1.5 AU. The major planets beyond act as a gravitational “shield”. The same conditions apply to other stars. They are all associated with a finite lifetime. Whether microbial life formed on Earth or whether precursors came from outside (transpermia), elemen- tary life was certainly present very soon after the formation of the Earth. Advanced and technologically-capable creatures required a much longer time to appear. Long timescales on Earth imply a lengthy, stable environment of solar radiation, stable planetary orientations and gravitational protection of the planet by one or more larger planets in exterior orbits. By implication, the orbit of the larger planet must have a semi-major axis at least as large as 2 AU and preferably rather larger. With the solar system in mind, interest now is with companions of this semi-major axis and of mass broadly comparable to that of Jupiter, MJ = 1.89 ×1027 kg. Observations so far suggest that the exoplanet systems have three general characteristics. First, there is usually one observed companion. Second, the semi-major axes are generally small, less than 0.1 AU. This leaves little room for smaller planets inside. Third, the eccentricities of the orbits are often not small but have values similar to those found for comets in the solar system. These characteristics seem incompatible with the conditions necessary for the development of advanced and technological life. There are, however, six systems where this is not necessarily the case (listed in table 1). While they each have a planet with a semimajor axis >2 AU, only one has a small eccentricity. 47 Ursa Major has two large companions with semi-major axes >2 AU, each with an essentially circular orbit. This star is 14 pc from Earth, which is about 44 ly (1 ly = 6.324 ×104 AU). The intense search for exoplanets since 1995 should have revealed companions with semi-major axes at least as large as 6 AU, but none have been found so far. It might be concluded that companions with physical characteristics able to support advanced life are few. Might there be a sphere of radius about 44 ly around the Earth where advanced life forms are very unlikely? This is a cell of volume 3 ×105 (ly)3 which might contain one “civilization”. The mean volume of an average galaxy is of Table 1: Star/companion systems with large semi-major axes System Stellar distance (pc) ε Eridani 47 Ursa Major 14 Her HD 190228 HD 10697 υ Andromeda MJ = 1.89 ×1027 kg Min. planet mass (MJ) 3.0 14.08 0.76 18.15 62.11 30.0 13.47 2.11 4.61 1 AU = 1.496 ×108 km Semi-major axis (AU) 0.8 2.54 3.73 3.3 4.99 6.59 0.71 0.83 2.5 1 pc = 2.06 ×105 AU 3.4 2.09 < 0.2 2.5 2.31 2.0 0.059 0.18 0.41 Amanda Baker and David Clements No room for complacency We were delighted to see several letters in the December 2001 issue of A&G, responding to our summary of the NAM2001 Careers Session. It was particularly gratifying to receive such enthusiastic support from three such diverse parties; indeed we, and I’m sure several others, were most tempted by Dr Harper’s description of life in bio-informatics. However, we are extremely disappointed (although, perhaps, not so very surprised) by the glaring absence of any response from 1.8 PPARC, any heads of department, or anyone else who sets policy concerning graduate students, postdocs and other fixed-term contract researchers (FTCS). This could be seen as an indication that policy makers have no interest in engaging with, let alone tackling, the very serious issues which we, and the other correspondents, raised. Would it be unfair to conclude that established academics have a deeply vested interest in maintaining the current iniquitous and damaging status quo? After all, those Orbital eccentricity 0.6 0.061 0.35 0.43 0.12 0.034 order 1015 (ly)3. There would be of the order 3 ×109 (1015/ 3 ×105) such cells in the galaxy. How many might contain a civilization? The answer would give an indication of the number of life forms present, independent of the Drake equation. Fossil remains of life on Earth reveal that microbial life appeared very soon after the formation of the planet, 4500 million years ago, and seems almost indestructible. Advanced life, by contrast, has been affected strongly by changing geophysical conditions. There have been several major extinctions (easily survived by microbia), and homo sapiens has appeared after a series of unlikely events – apparent accidents. It is possible that evolutionary forces and external physical events will limit the life span of the species. The Sun itself has only a finite life anyway. Such considerations can be expected to apply elsewhere, suggesting that microbial life might be universal but advanced life, being vulnerable, may be rare and limited. If one cell in a hundred develops advanced animate forms, there could be of the order 3 ×107 “civilizations” in the galaxy. If only one in a million does so, the number is approximately 3 ×104. Each has a finite lifetime, though it may be lengthy. These are relatively small numbers; they become enormously large if other galaxies are included. The mean distance between cells remains always large, effectively isolating them. There would, anyway, be no evolutionary advantage of contact-at-a-distance since there is then no mixing of genes, necessary for a universal application of Darwinian arguments. G H A Cole, University of Hull, Hull, HU6 7RX. [email protected] privileged few academics on openended contracts can thereby acquire cheap, virtually disposable labour to work on their research projects, and advance their RAE ratings, with no need to devote significant effort to the career development or long-term aspirations of at least three-quarters of their graduate students and FTCS. While the infamous Concordat is meant to address some of these issues, it is telling to note that a recent study (Academic Research Careers in Scotland, SHEFC) showed that the majority of contract researchers do not even know of its existence. The reality on the ground is that academics routinely fail to provide adequate (or indeed, any) career guidance for their graduate students and FTCS; meanwhile, university careers services are woefully ill-prepared to meet the very real needs of these people when their research supervisors fail them. In fact, only 12% of contract researchers in the SHEFC study received any form of formal careers advice or guidance. If there is a real desire for reform on the part of the astronomy and geophysics “establishment”, much more must be done and there must be a dialogue between those who set policy and those who are subject to fixed-term contracts. This will be especially true as universities and February 2002 Vol 43 VIEWS M Iftikhar Ahmad The New World Calendar The Gregorian calendar was introduced in March 1582 by Pope Gregory XIII. It was subsequently adopted by various countries at different times. Great Britain adopted it on 2 September 1752, whereas Russia didn’t adopt it until 1917. At present almost every country in the world uses this calendar. The Gregorian calendar has a number of drawbacks. The Earth revolves around the Sun and completes one revolution in 365 days, 5 hours, 48 minutes and 46 seconds; i.e. the length of one tropical year is 365.2422 days. This fractional part makes the formulation of the calendar difficult – although the Gregorian calendar is better than the Julian calendar, as the average duration of the year improved from 365.2500 to 365.2425 days. The difference, therefore, between the average duration of the Gregorian year and the length of the tropical year remains 0.0003 days instead of 0.0078 days. However, this means that the Gregorian calendar is out by 0.0003 days per year, which will amount to 3 days in 10 000 years. A calendar needs to be devised in such a way that the average duration of a year is exactly equal to the length of a tropical year. A solution of the above problem is given in “Refinement of the Gregorian calendar” (M Iftikar Ahmad 1992 J. Sci. Res. P U Lahore, Pakistan XXI 1&2 57–63) where the following formula is suggested: A year divisible by four will be a leap year, provided that it is not a multiple of 100. In the case where a year is a multiple of 100, it will be a leap year only if the number obtained by suppressing the zeros on the right is divisible by four. By this formula, the years 2000, 6000 and 10 000 would not be leap years, despite being divisible by 400, as they are according to the Gregorian calendar. In this way, the 3 days difference in 10 000 is adjusted. Similarly, during the following 10 000 years, the years 14 000, 18 000 and 20 000 would not be leap years, and the average duration of the calendar year is reduced to 365.2422 days per year. This agrees with the length of a tropical year. The formulae set out above are based on the assumption that the length of a tropical year is constant, whereas according to the Explanatory supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac, 1961 it is shrinking and even the new formula given above will eventually get out of step. The shrinkage according to the formula is given by table 1, where T is the time in Julian centuries from the epoch; the terms in T2 and T3 in the 1992 edition are too small to affect the discrepancy. This means that the tropical year is shortening in days by 0.0000614 per millennium. The Gregorian calendar is haphazard in the sense that the number of days in a month varies from 28 to 31. They should be equal in length as far as possible. It is important from the point of view of business and banking that the year research councils change their policies to respond to the new regulations from the EU Directive on Fixed Term Work (www.dti.gov.uk/ er/fixed/) which, at face value, would suggest that many of the iniquities arising from fixed-term contracts are to be made illegal. These issues go to the heart of the way science operates in the UK. The problems produced by inappropriate dependence on fixedterm contracts are now being examined by several influential bodies beyond astronomy and geophysics (e.g. SHEFC report, Quinquennial Review of Research Councils, The Roberts’ Review) and are being raised at the highest levels (e.g. the Scottish Parliament, the House of Lords). Comparison with the USA is telling. According to preliminary results of a longitudinal AAS study (Marvel et al., private communication) 68% of astronomy PhDs are still working in the subject seven to nine years after completing their thesis. This compares to PPARC’s figure of 25% of UK astronomy PhDs obtaining “permanent posts” in the field. The simple conclusion from these figures is that anyone wanting a long-term career in astronomy should avoid UK universities and move to the US for their PhD. And yet we hear nothing from PPARC or anyone else in the February 2002 Vol 43 Table 1: Shortening of the tropical year Edition Epoch Days 1974 1900 365.24219878 – 0.00000614 T 1992 2000 365.2421896698 – 0.00000615359 T – 7.29 ×10–10 T 2 + 0.000… Table 2: Accounting for the shortening tropical year i 1 2 3 4 5 6 7 Pi AD 2001–7000 AD 7001–12000 AD 12001–17000 AD 17001–22000 AD 22001–27000 AD 27001–32000 AD 32001–37000 λi 3200 2800 2400 2000 1600 1200 800 should be divided into as near as possible four equal quarters, each of three months. In the Gregorian calendar, the first, second, third and fourth quarters of a normal year are of 90, 91, 92 and 92 days respectively. In view of all these deficiencies, the Gregorian calendar is not compatible with the present age, and in the New World order, a new calendar is required. This calendar should be devised in such a way that it removes the defects of the present calendar and at the same time is simple, regular, uniform and meets all other requirements as far as possible. Keeping in view all these considerations, the following calendar is suggested: ● The first month of every quarter and the last month of the year, i.e. January, April, July, October and December, will each have 31 days. ● The remaining months, i.e. February, March, May, June, August, September and November, will each have 30 days. ● In leap years, June will have 31 days. By increasing the length of June by one day, the quarters of 91 and 92 days will be placed alternately during the leap year. To make this calendar conform with the changing tropical year, the following formula is suggested: ● A year divisible by four will be a leap year, provided it is not a multiple of 100. ● In the case where a year is a multiple of 100, then it will be a leap year during the period Pi if it is divisible by 400 but not by λi , where λi forms an arithmetic progression as given in table 2. Note that by the year AD 37 000, the length of a tropical year will become 365.2400 and no century year will be a leap year. astronomy and geophysics “establishment” concerning these issues. If this silence genuinely reflects the level of interest that PPARC has in the career development of its postdocs, then it is probably time for us all to contact organizations such as The Sanger Institute and look into new areas of work in which something deserving of the name “career” is possible. Academic Research Careers in Scotland www.shefc.ac.uk/content/shefc/research/crs/ CRS.html DTI Website www.dti.gov.uk/er/fixed/ Quinquennial Review of the Research Councils 2001, DTI. Sir Gareth Roberts Review of the Supply of Scientists and Engineers (due to report for HM Government in Feb 2002) www.hm-treasury.gov .uk/Consultations_and_Legislation/ Review_of_ the_Supply_of_Scientists_and_Engineers/ Motions to Scottish Parliament S1M–2184 and S1M–2368 Hansard 28 11 2001, Col 369. Amanda Baker, Cardiff; David Clements, London. References A Concordat to provide a framework for the career management of contract research staff in universities and colleges www.dti.gov.uk/ost/concord.htm M Iftikhar Ahmad, Lahore, Pakistan. ● Note that this year’s NAM will have a Careers Session as well as other forums for discussion of these issues. www.star.bris.ac.uk/nam/index.html 1.9