Tag Archives: space

An unexpected hazard of manned Mars exploration

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mars-surface

There are many risks associated with a manned mission to Mars. The journey itself would last between 150 and 350 days, and beside the risks associated with prolonged isolation and cramped conditions there is also the lack of real-time communication caused by the time taken for radio signals to travel the very large distances involved. Once arriving on Mars there is the presence of high levels of cosmic rays and ionising radiation to content with, all to be dealt with without proper medical facilities.

But a new paper* identifies a risk I hadn’t considered: asteroid impacts. Mars is much closer to the asteroid belt than Earth, and thus asteroid impacts are more frequent. The authors analyse the rate of crater formation on Mars and come up with a model that predicts the number of craters of a given diameter likely to be formed over a given period of time.

crater-impact-graph

Their model predicts that a one megaton (≈1 km crater) impact will occur once every 3.3 years, which would make spending any significant length of time on Mars quite hazardous. Mars’ atmosphere is much thinner than Earth’s, with an atmospheric pressure only 0.6% of ours, and so damage on the Martian surface is likely to be much more severe than for a similar impact on Earth.

* William Bruckman, Abraham Ruiz and Elio Ramos, “Earth and Mars crater size frequency distribution and impact rates: Theoretical and observational analysis”, arXiv:1212.3273.

Cosmic Latte

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Cosmic Latte is the jokey name given to the overall colour of the Universe. If all the different wavelengths and intensities of light in the Universe were added together, the result is the light beige colour seen above.

The raw data from the study* is shown below.

Click to enlarge

A number of peaks are visible in the spectrum, in particular the H-alpha line emitted by ionised hydrogen gas.

* Ivan Baldry et al, “The 2dF Galaxy Redshift Survey: Constraints on Cosmic Star Formation History from the Cosmic Spectrum”, The Astrophysical Journal 569:582-594 (2004). DOI: 10.1086/339477.

You can see more than half of a neutron star

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Common sense dictates that if you look at a spherical object like a ball or a planet you can only see half the surface area of that object. But this is not true for neutron stars.

A neutron star is formed when the core of a relatively large star collapses in on itself in a supernova. Neutron stars are incredibly dense: one teaspoon of neutron star can have a mass of more than five trillion kilograms.

One of the best elaborations of Einstein’s Theory of General Relativity was given by John Wheeler:

“Mass tells space-time how to curve, and space-time tells mass how to move.”

But if space-time is curved then anything passing through space, whether it is matter or light, will follow a curved path. The gravitational field of a neutron star is so strong that it warps space, and warps space to such an extent that light emitted behind the star is warped around.

Diagram of a neutron star, viewed face-on.

In the diagram above each chequered section is 30° × 30°; note that both poles of the neutron star are clearly visible. The highlighted section on the right-hand diagram shows the area that would normally be visible if gravitational distortion were not present.

Normally 180° of latitude and longitude would be visible, but in this case the figure is nearly 260°, meaning that more than 70% of the neutron star’s surface area is visible.

Salt flats and giant space mirrors

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A salt flat is formed when a pool of salt water evaporates, depositing salt as it does. This layer of salt builds up over time and seasonal flooding causes a very flat surface to form.

Salar de Uyuni in Bolivia, the largest salt flat in the world.

When covered in water, salt flats become the largest mirrors in the world.

Salt flats are commonly used to calibrate observation satellites, as they provide very large and flat areas (Salar de Uyuni has an area of more than 10 000 square kilometres and varies in height by less than one metre). The surface of salt flats are highly reflective and because they occur in desert areas there is usually very little cloud cover and very clear air.