Subscribe to our free daily newsletters
. 24/7 Space News .

Subscribe to our free daily newsletters


This is a 2.07 micron image of Jupiter taken on the NASA Infrared Telescope Facility, Mauna Kea, Hawaii, at 08:54 on July 21, 1994. The image was taken in a four second exposure using the IRTF's facility near infrared camera, NSFCAM. Io, the closest of the jovian moons, can be seen crossing the planet in the northwest of the image (top right). The Great Red Spot is visible in the south east of the planet. At the collision latitudes, the impact due to Fragment Q is just setting on the west. Just to the east of it, the R Fragment impact site shows up very brightly. Another four impact sites form a chain of spots behind R (N.B there is an additional fainter spot which may not be clearly visible). Steve Miller and Mark Shure for the NASA IRTF Comet Science Team

Protected By Gas Giants
by Bruce Moomaw
Cameron Park - May 2, 2000 - Without those two planets (and especially Jupiter), there would be thousands of times more comets in the "Kuiper Belt", a relatively short distance outside the giant planets.

And they would wander into the inner Solar System so frequently that such impacts might completely devastate Earth as often as once every 100,000 years -- enough to make absolutely certain that metazoan life would never have the slightest chance to even start evolving on this planet.

Moreover, the fact that we have gas giants big enough and appropriately placed to serve as our protectors is by no means a high probability, especially given the fact that most gas giants apparently migrate a good distance inward from where they fist formed.

Indeed, Wetherill's simulations have shown that smaller Uranus-sized gas giants at the same distance would instead deflect the orbits of comets just enough to substantially increase the number of comets entering the inner Solar System instead!

In his own Conference talk, John E. Chambers announced still another possible complication.

The growing feeling is that the near-Sun rocky debris from which the inner planets formed was very short on water, and that the water supplies of early Venus, Earth and Mars came mostly from the barrage of icy outer Solar System objects that did hit those planets during the Solar System's early "heavy bombardment" period.

But with Jupiter and Saturn clearing out most of the comets that would otherwise have entered the inner System, the only adequate supply of such icy objects would be the asteroids from the outer half of the Asteroid Belt -- and Jupiter's gravitational tuggings also tended to nudge many of those into entering the inner System and colliding with the inner planets.

Had Jupiter been even moderately farther from the Sun, it would still have protected the inner planets from a huge overdose of comets -- but it might also have deprived them of the early rain of icy asteroids that gave them most of their water. On the other hand, if Jupiter was moderately closer to the Sun -- say, within 450 million km -- its tuggings would have either thrown the inner planets into disastrously eccentric orbits or prevented the rocky debris in the inner System from coalescing into planets at all, so that the Solar System's inner rocky parts would just hae consisted of an asteroid belt.

As Chambers told me, "Jupiter and Saturn are fortunately placed."

So what does all this mean for the chances of complex life elsewhere in the universe? Ward repeated his and Brownlee's belief that there are very large parts of the universe that are "deserts" as far as the development of complex life is concerned.

During the universe's early days, the first generation of stars had not yet converted its initial hydrogen and helium into "metals" (by which astrophysicists mean all elements heavier than helium) -- so there was very little solid material, even ice, from which planets of any kind could develop.

During the universe's distant future, billions of years from now, the supply of uranium, thorium and radioactive potassium -- which provide the internal heat that drives a planet's crustal tectonics and volcanism -- will have greatly shrunk; and without such crustal recycling it will be almost impossible for a planet to maintain the atmospheric carbon dioxide that it needs to maintain and stabilize its climate at a good temperature for life.

(Even large rocky planets will then behave like Mars.)

And even today, small non-spiral galaxies are thought to be poor in "metals", as are the outer regions of spiral galaxies -- including our own -- making planets much rarer in them.

  • Click For Part Four

    Thanks for being here;
    We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

    With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

    Our news coverage takes time and effort to publish 365 days a year.

    If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

    SpaceDaily Contributor
    $5 Billed Once

    credit card or paypal
    SpaceDaily Monthly Supporter
    $5 Billed Monthly

    paypal only

    Memory Foam Mattress Review
    Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
    XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

  • The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.