Shoemaker-Levy 20th Anniversary

Impact of comet with Jupiter

Image of Jupiter taken by Peter McGregor 12 minutes after an impact.

20 years ago, comet Shoemaker-Levy 9 made headlines around the world when it crashed into Jupiter. The impacts produced the biggest planetary explosions scientists have ever seen.

Astronomers were able to calculate that Shoemaker-Levy 9 had passed so close to Jupiter two years before impact that the giant planet’s powerful gravity had pulled the comet apart into fragments.

Shoemaker-Levy 9 Fragments

Shoemaker-Levy fragments flying through space two months before impact. Fragment G caused the explosion shown in the image page top. Hubble Image from NASA.

Don’t make the mistake that the word ‘fragment’ here means these were tiny particles. Three of the fragments were 1 km or more across.

This was a science story so big that it made headlines all over the world. The single explosion shown page top released the same amount of energy as a simultaneous detonation of 400 million Hiroshima sized nuclear bombs.

Jupiter’s clouds were left with dark scars where the impacts took place, which lingered for weeks.

Jupiter following the impacts. The dark patches caused by the impacts are almost Earth sized.

Jupiter following the impacts. The dark patches caused by the impacts are as big as planet Earth.

You can read more about the impacts on our Gene Shoemaker page.

So, What’s Been Happening Since?

Just last year, the Herschel Space Observatory captured this image, showing water in Jupiter’s stratosphere.

Water in Jupiter's Stratosphere

Image by ESA/Herschel/T. Cavalié et al.; Jupiter image: NASA/ESA/Reta Beebe (New Mexico State University)

A minimum of 95 percent of this water actually came from Shoemaker-Levy 9 when it vaporized in Jupiter’s atmosphere. The highest water concentrations are in the cyan/white areas of the image. The highest concentrations are in Jupiter’s southern hemisphere, where the comet struck.

Clearly, after 20 years, Jupiter is still feeling the effects of the comet impact!

But Wait, There’s More (Impacts)

Most of the scientists who were involved in the Shoemaker-Levy 9 observations felt they were watching a once-in-a lifetime event. However…

In 2009, astronomy enthusiast Anthony Wesley was imaging Jupiter from his backyard in Murrumbateman, Australia. A dark patch caught his eye, a patch which reminded him of one of the biggest astronomy stories he’d known in his life.

It looked very much like the scars he had seen on Jupiter from Shoemaker-Levy 9’s impacts.

Anthony Wesley quickly let the world’s astronomy community know what he had seen.

Telescopes around the world turned to focus once again on Jupiter.

And, sure enough, there it was… a new impact scar.

jupiter impact scar 2009

Jupiter scar from impact in 2009. NASA image from the Hubble Wide Field Camera 3.

Experience with the Shoemaker-Levy 9 impacts allowed astronomers to estimate the object that hit Jupiter in 2009 was a few hundred meters across.

So what else does the 2009 impact tell us?

The 2009 collision means that:

Either impacts are much more frequent than astronomers thought. Most astronomers thought there wouldn’t be another major impact on Jupiter for hundreds of years…


We’ve been lucky to see such rare impact events twice within the space of 15 years.

I don’t know about you, but personally, I’m hoping it’s the latter of these two possibilities!


Your Genes Programmed by your Ancestors’ Terror

DNA and memory

One of your ancestors had a terrifying experience? New research shows your genes might have a memory of this terrifying experience built into them, and you may fear the same thing happening to you.

But that’s now how genes should work, is it?

To understand this, we’ll begin by considering identical twins, who are born with identical genes.

Over time, their bodies and behaviors become increasingly different, more so if they grow up in different environments, having different experiences.

What happens to us in life changes the way our genes behave – this is called gene expression. What you do, what you eat, how you exercise, even the music you listen to alters your gene expression.

There’s no doubt that terrifying experiences also change our gene expression. This is accepted science. The behavior of the genes in our bodies changes with our experiences.


In technical terms, your inbuilt, inherited genes, called your genotype, are influenced by gene expression to determine your phenotype. Your phenotype is YOU – the way you develop, and behave, your internal biochemistry, the way you think, and what you do with your time each day.

It’s already well-known that if one family member has a phobia, then the levels of this phobia among first-degree family members will be much higher than average, by a factor of more than x10.

More recently, scientists have claimed that terrifying experiences do not only affect your phenotype, they actually get built into your genes and can be passed on as an inherited fear to your offspring and generations to come.

Barry Dias and Kerry Ressler from Emory University School of Medicine exposed mice to fearful experiences (electric shocks) while there was a smell of cherry blossom around.

We’d normally expect this would alter the mice’s gene expression, affecting their behavior – their phenotype. We would not expect it would fundamentally change their genotype, their basic genetic code that would be passed on to future generations.

BUT it turns out that the mice’s offspring and the offspring’s offspring were still fearful of the scent, even though they had never smelled it before and had no reason to fear it.

The brains of the parent mice were found to have been changed by their experiences, and the offspring also showed the same changes to their brains.

This is evidence that a parent’s experiences can be written into the parent’s genetic code, then passed on to the children and later generations. If an ancestor of yours had a bad experience, you might also fear that experience, even if you have no reason to fear it from your own experiences.

Your own fears, such an unusual terror of spiders, heights, open spaces, or closed spaces, etc, may come from something that happened to a parent, grandparent, or someone further back in your family tree.

This is a rather extraordinary claim, and does not fit with our current understanding of evolution by natural selection.

It’s a basic tenet of science that the more extraordinary the claim, the higher the level of proof that is required. So don’t go expecting that the evidence from this single study will be enough to change the textbooks. More studies will be required for that to happen.

All the same, it’s very interesting, and science does thrive on interesting new phenomena.

Much more speculatively, the research also raises the possibility that other memories of our ancestors could have been built into their genes and passed on to us.

If this were true, claims of people to have memories of previous lives may need to be revisited… but this really is entering the realms of fantasy, isn’t it?