Category Archive: Space

Space coverage on this site concentrates on planetary science and the small bodies of the solar system, and it is written on the assumption that the interesting question is what an instrument can actually measure — not how far away the object is.

Why small bodies

Planets are reprocessed worlds. Heat, pressure, weather and tectonics have destroyed most of the chemical record of how they formed. Asteroids and comets have largely escaped that: many are effectively unaltered material from the disk out of which everything else condensed, preserved for four and a half billion years because they were never big enough to melt.

Reading them is the closest available approach to reading the initial conditions. That is why so much mission time is spent on objects that look, in a released image, like grey potatoes. The photograph is not the product; the spectra, the mass estimate and the crater statistics are.

The economics of the flyby

Interplanetary missions spend years cruising between arrival events, and a trajectory can often be nudged to pass close to a target of opportunity for a modest fuel cost. The spacecraft is already built, the instruments are already aboard and the operations team is already funded, so the marginal cost of an entire secondary science campaign can be very small.

A large share of what is known about small bodies came from exactly this arrangement — missions bound elsewhere, taking the long way round on purpose. See 21 Lutetia, where a comet-bound probe passed within about two thousand miles of a main-belt asteroid whose classification had resisted decades of telescope work.

What a close pass settles

Ground observation gives brightness, colour, a rotation period and a crude size. It cannot give shape, density, surface texture or the distribution of craters. Those come only from proximity, and they are what distinguishes competing hypotheses — a primitive carbon-bearing body versus the exposed remnant of a larger object that was broken apart look similar from Earth and completely different from two thousand miles.

Density is the sharpest discriminator, and it comes free with the encounter: the spacecraft's own deflection as it passes gives the object's mass, and mass with a measured volume gives density. A porous rubble pile and a solid metallic fragment cannot be confused once that number exists.

Reading mission news carefully

Two habits protect a reader from the worst of space coverage. First, distinguish a raw image released within hours from the processed science published months later; the first is a public-relations artefact and the second is the result. Second, treat any single-mission conclusion as provisional until an independent measurement agrees, because the sample size at these distances is frequently one.

In this archive

• 21 Lutetia — the largest asteroid visited by a spacecraft at the time of the encounter, and what the flyby was expected to settle.
• U.S. Navy Laser Weapon Shoots Down Drone in Test — adjacent technology: beam control, atmospheric propagation and precision tracking.

Mission documentation referenced here is published by the European Space Agency; designations and orbital elements for every catalogued small body are maintained by the IAU Minor Planet Center, under the naming authority of the International Astronomical Union.

Browse also: World, Sanctions, the July 2010 archive, or the front page.

Why space stories are reported badly

Space coverage fails in a consistent way: the release of an image is treated as the result, and the actual result — published months later in a form that requires effort to read — is not covered at all. An agency's communications office is measured on attention, so it publishes the picture immediately; the science team is measured on peer review, so it publishes when the analysis is finished. Only one of those two events is convenient for a news cycle.

The consequence is an audience that has seen a great many pictures and learned very little. The corrective is to report the question a mission is designed to answer before the encounter, and then return when the answer exists.

A note on distances and scale

Coverage of small bodies routinely invites confusion about scale. A pass at two thousand miles sounds close and, in the context of a body a hundred kilometres across, it is — closer than most Earth-observation satellites are to the ground. The asteroid belt itself is the opposite: despite the imagery it inspires, its members are separated by such distances that a spacecraft crossing it is in no meaningful danger of collision, and reaching any specific one requires the encounter to be planned years ahead.