Cosmiques Arête: grade, duration and exit at the Aiguille du Midi

The Cosmiques Arête is graded AD, fairly difficult, with engagement II and equipment P2 on Camptocamp. The rock is graded 4a free and 3c obligatory, and Alpine Mag gives the same overall grade. That grade sits above both normal routes on Mont Blanc, the Goûter route graded PD− and the 3 Monts traverse graded AD−, on a far shorter outing. The ridge is a day of technique, not a day of endurance.

The route adds up to 300 m of ascent and 300 m of descent, of which 240 m of difficulties that begin at 3,600 m and end at 3,842 m. Its lowest point is 3,550 m, its aspect south-west. The start is taken at the Cosmiques hut, at 3,613 m on the col du Midi glacier, open from mid-February to late September. The exit is on the summit terrace of the Aiguille du Midi, 65 m above the cable car's upper station, built on the Piton Nord at 3,777 m.

Three passages shape the route. The approach descends the snow ridge from the station to the col du Midi, then gains the Simond shelter. The middle section is passed on rappel at the gendarmes: the Passion Alpes topo describes rappels of 10 m, 15 m and 20 m on the south side, the classic choice when the ridge holds snow, and gives a north-side option when it is dry. The final step is a compact slab scored by an oblique crack, climbed with crampons on at M3+/4a, followed by a runnel, a mantelshelf, then a ladder that comes out on the terrace of the aiguille. The Compagnie des Guides de Chamonix describes that section as a 5-metre crack scoring a smooth wall. The Simond shelter, at 3,593 m on the ridge, was built in 1942 to house the workers building the cable car's upper station and carries the name of Alfred Simond, a guide and hunter who died in early 1940. The ridge itself takes its name from the cosmic-ray laboratory that the physicist Louis Leprince-Ringuet set up at the col du Midi.

Allow 30 minutes of approach and 2 to 4 hours on the route. The Passion Alpes topo ties that twofold spread to traffic. Camptocamp counts the route as a single day and sums it up as a fine high-altitude classic, neither very long nor very difficult, but very and even too busy. The crowding comes from the access. The Aiguille du Midi cable car carried 878,411 passengers in 2014; the Compagnie du Mont-Blanc advertises a cabin every 10, 15 or 30 minutes depending on demand. A party that wants to reach the rappels without queueing therefore takes the first cabin, or sleeps at the hut the night before.

On the 2026-2027 winter timetable published by the Compagnie du Mont-Blanc, the Aiguille du Midi opens at 08:10, the last round-trip ascent leaves at 15:00, the last one-way ascent at 16:00 and the last descent at 16:30. A footnote on the same timetable announces a 07:30 opening on weekends, public holidays and long weekends in March, April and May 2026. The operator states that these times are indicative and can change with operating constraints or weather. The summer timetable was not published at the last check of this page: the time of the first summer cabin, the one that decides whether a party can go in a day, has to be checked directly with the Compagnie du Mont-Blanc. The last descent remains the hard constraint of the day, since the route finishes on the terrace and not in the valley.

The route description on Camptocamp now holds nothing but a warning: following the rockfall of 22 August 2018, consult the information given by La Chamoniarde, which published a document describing the variant in 2019. Earlier topos therefore no longer describe the ground as it stands today. La Chamoniarde runs the Office de haute montagne and a mountain conditions feed, to be read before going up. The Passion Alpes topo adds a seasonal constraint: the ridge is climbed in crampons as long as it holds snow, generally until around mid-June, and calls for care when it is dry because of rockfall.

The route has you sleep at 3,613 m and climb to 3,842 m, which is 7 m above the Goûter hut (3,835 m) and still 965 m below the summit of Mont Blanc (4,807.47 m). It serves as a technique and acclimatisation step, not as an altitude test. The Compagnie des Guides de Chamonix schedules it over two days with a night at the Cosmiques hut and reserves it for people wanting an introduction to mixed mountaineering who already have cramponing experience, with 2 clients per guide. Since the hut is also the base camp for the 3 Monts traverse, a party can climb the ridge one day and leave for Mont Blanc the following night from the same hut. Three things are still missing from that programme: the long day of the 3 Monts route, progress on crevassed glacier, which the ridge does not drill, and real tolerance above 4,000 m, which no outing at 3,842 m validates.