$natural in reverse order into aggregation stage

MongoDB University M121: The MongoDB Aggregation Framework
#1

Can I sort documents in reversed natural order using aggregation framework?
With the query framework I can specify:

db.solarSystem.find().sort({$natural: -1}).limit(5).pretty()

Thanks.

#2

I was going to answer that you can with the following.

{ $sort : { $natural : -1 } } should be a valide pipeline stage.

But I tested it with the following minimal example:

> var sort = { '$sort' : { '$natural' : -1 } }
> var pipeline = [ sort ]
> db.test.aggregate( pipeline )

But I got:

	"errmsg" : "FieldPath field names may not start with '$'.",