COVER Two samples of rock (top and bottom holes) were collected by the Perseverance rover from this outcrop of the Séítah geologic formation in Jezero crater, Mars. Also visible are a discarded sample attempt (middle hole), a rock abrasion patch (lower left depression), and the rover’s tracks and shadow. Analysis of the Séítah formation shows that it consists of igneous rocks modified by liquid water. See pages eabo2196 and 1513.

Photo: NASA/JPL-Caltech

ONLINE COVER A proposed “roll-to-roll” method of lithium recycling. The abundance of used batteries containing lithium offers a key source of the metal for sustainable battery production. However, recycling lithium often causes degradation of quality. Xu et al. propose a sustainable lithium recovery strategy for spent batteries. The system relies on electrical current driven diffusion to separate out usable lithium and can achieve repeated recycling without destroying the metal’s integrity. This method of lithium recycling has low energy consumption and could have high economic and environmental benefits.

ONLINE COVER Waves of IgA Regulate the Intestinal Microbiota. This month’s cover depicts the dynamic interplay between immunoglobulin A (IgA) and the commensal microbiota in the intestinal lumen. Penny and Domingues et al. report that secretory IgA exhibits daily rhythms in its release from lamina propria plasma cells into the intestinal tract, which are controlled by signals provided by food and the circadian clock. These “waves” of IgA regulate the daily oscillations in the relative abundance of commensal gut microbes to help maintain gut homeostasis.

ONLINE COVER Microrobots Make Big Steps Toward Autonomy. Existing microrobots are generally limited to external control through magnetic fields or light. Microrobots that are able to integrate control, power, and sensing internally (or onboard) are expected to achieve greater autonomy than their externally controlled counterparts. Reynolds et al. have built microscopic robots controlled by onboard complementary metal oxide semiconductor (CMOS) electronics. These microrobots are powered by light and use onboard computers to execute pre-programmed motions. This month’s cover is a false-color scanning electron microscope image of microscopic robots before release.

ONLINE COVER This week, Kong et al. show that the kinase PLK1 promotes the growth of some lung cancers by stimulating the expression of RET, which encodes a receptor kinase that increases the activity of a tumor growth–promoting pathway. The image shows stained lung tissues from mouse models of KRAS-mutant lung adenocarcinoma.

ONLINE COVER NO Change in the NOSe. This image of transient axonal glycoprotein 1 (TAG-1) staining reveals normal olfactory bulb morphogenesis and olfactory fiber projections in a mouse lacking expression of the gene encoding nitric oxide synthase 1 (NOS1). Chachlaki et al. studied the role of NOS1 in congenital hypogonadotropic hypogonadism (CHH), finding that NOS1 activity affected the number of gonadotropin-releasing hormone-producing neurons and their migration in the developing mouse brain, whereas olfactory bulb morphogenesis was maintained. Nos1 deficiency in mice resulted in defects in sexual maturation, olfaction, hearing, and cognition, mirroring the findings in six humans with CHH caused by NOS1 mutations. Administration of sildenafil or inhaled nitric oxide during minipuberty could ameliorate these symptoms in Nos1 mutant mice, suggesting a potential treatment for humans with NOS1 mutations.