More than 200 years ago, mathematician Joseph-Louis Lagrange predicted the existence of what became known as Trojan asteroids  small bodies that can stably share the orbit of a planet if they remain near ‘triangular points 60° ahead of or behind it in its orbit. Jupiter has thousands of Trojans; Mars and Neptune have some too. Now Earth is shown to have a Trojan. A search of data collected by NASA’s Wide-field Infrared Survey Explorer (WISE) satellite revealed the asteroid 2010 TK7 as a strong candidate, and subsequent optical observations confirm its status as a Trojan companion of Earth, oscillating around the L4 (leading) Lagrange triangular point. The cover imagines 165 years of motion of 2010 TK7 seen from a vantage point outside of, and above, Earth’s orbit. Cover image: Paul Wiegert.

The type VI secretion system (T6SS) is a protein-export machine that is present in about one-quarter of all sequenced bacteria. Bacteria can use this system to deliver toxic effector proteins in a contact-dependent manner to other bacterial cells. However, what these proteins do once their destination is reached has remained largely unknown. It is now shown that the opportunistic human pathogen Pseudomonas aeruginosa uses its T6SS to kill competing Gram-negative bacteria by injecting them with two peptidoglycan-degradative enzymes, the effector proteins Tse1 and Tse3. P. aeruginosa protects itself from these effectors by expressing immunity proteins that bind the toxins. A clash between bacteria is depicted on the cover. T6SS effector proteins transferred from a donor (red) to a recipient cell (green) degrade the cell wall, resulting in a breach in the peptidoglycan layer of the recipient. The outer membrane of the duelling Gram-negative bacteria is not shown, so that the underlying peptidoglycan layer is visible. Cover graphic: Jaime Easter.

The genome of the potato (Solanum tuberosum L.), a staple crop vital to food security, has been sequenced. The Potato Genome Sequencing Consortium sequenced a homozygous doubled-monoploid potato clone as well as a heterozygous diploid clone. Genome analysis reveals traces of at least two genome duplication events and genes specific to Asterids, a large clade of flowering plants of which the potato is the first to be sequenced. Gene presence/absence variants and other potentially deleterious mutations are frequent and may be the cause of inbreeding depression. The genome sequence will facilitate genetic improvements in the potato with a view to improving yield and to increasing disease and stress resistance of this crop, which is a now a significant component of worldwide food production and is becoming increasingly important in the developing world.

Six Great White Spot (GWS) events have been observed in the atmosphere of Saturn since 1876. These giant convective storms occur roughly once every Saturnian year (equal to 29.5 Earth years). The sixth GWS erupted in December 2010 and has been the subject of intense observation. Two papers in this issue present the details of some of these observations. Sánchez-Lavega et al. report that the storm developed at northern latitudes in the peak of a weak westward jet during early northern springtime. The storm head moved faster than the jet and triggered a disturbance that circled the planet. Numerical simulations show that Saturn’s winds extend without decay deep down into the weather layer. Fischer et al. report that the storm reached a width of 10,000 kilometres within three weeks. Its lightning flash rates are an order of magnitude greater than those seen in previous storms, peaking at more than 10 flashes per second. In the cover image, taken on 25 February 2011, the clouds have formed a tail that wraps around the planet. Image: C. Porco and CICLOPS (NASA/JPL-Caltech/SSI).